System and method for identifying a landmark

ABSTRACT

A field generator for use in a surgical targeting system is disclosed. The field generator includes a mounting structure including elements that are configured to receive components of an electromagnetic field generator. The elements are disposed on the mounting structure at locations and orientations relative to each other. The field generator includes at least one covering formed over the mounting structure, wherein, in use, the locations and orientations of the elements relative to each other remain substantially unaltered after exposure to one or more sterilization processes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a is a continuation of U.S. patent application Ser.No. 14/580,579, filed Dec. 23, 2014, now allowed, which is a divisionalof U.S. patent application Ser. No. 12/768,689, filed Apr. 27, 2010, nowU.S. Pat. No. 8,945,147, which is a continuation-in-part of U.S.application Ser. No. 12/547,716, filed Aug. 26, 2009, now U.S. Pat. No.8,784,425, which claims priority from U.S. Provisional Application Ser.No. 61/173,069, filed on Apr. 27, 2009. The entire contents of the priorapplications are incorporated herein by reference.

BACKGROUND

Technical Field

This disclosure relates to identification of blind landmarks onorthopedic implants.

Description of the Related Art

The interlocking nail has significantly widened the scope forintramedullary (IM) fixation of long bone fractures. Anchoring an IMnail to a bone makes the construct more stable longitudinally and stopsrotation of the nail within the bone. A typical IM nail fixation surgeryinvolves a combination of jigs, x-ray imaging, and manual “eye-balling”to locate and drill the distal screw holes and to install the screws inthe screw holes.

In IM nail fixation surgery, an IM nail is inserted into the canal of afractured long bone in order to fixate the fractured ends together.Typically, the proximal locking is performed first and is usuallycarried out with a jig. Nail deformation during intramedullaryinsertion, however, may make a jig inaccurate for the distal screws. Infact, the positioning of the distal locking screws and alignment of thedrill for the drilling of the distal screw holes is the most timeconsuming and challenging step of the implantation procedure. The twomain reasons for failure in distal locking are (1) incorrect entry pointon the bone and (2) wrong orientation of the drill. If either of theseproblems occurs, then the drill will not go through the nail hole. Aninaccurate entry point also compounds the problem as the rounded end ofthe drill bit often slips, damaging healthy bone rendering it difficultto place another drill hole next to the inaccurate hole. Inaccuratedistal locking may lead to premature failure with breakage of the nailthrough the nail hole, breakage of the screw, or the breaking of thedrill bit within the bone.

Manual techniques are the most common and accepted techniques forsighting the distal screw holes. The majority of manual distal targetingtechniques employ a guide bushing or cylindrical sleeve that guides thedrill. The mechanisms of aligning the guide bushing and keeping it inplace differ. There are cases where the surgeons use a guide bushing cutin half longitudinally or a full guide bushing to help steady the drillbit. In either situation, the surgeon will incise the patient and insertthe drill through the incision. Manual techniques are based primarily onthe surgeon's manual skill and make use of radiographic x-ray imagingand mechanical jigs.

Another method for achieving this on long nails is by using a techniquecalled “perfect circles” with the aid of a C-shaped arm. This is wherethe patient and the C-arm are oriented such that when viewing theimplant fluoroscopically the hole through which the screw is to passappears to be in the shape of a circle. If the C-arm is notperpendicular to the hole then the hole appears oblong or even absent.

A need exists for an improved system and method for accurately anddependably targeting landmarks of a medical implant. Further, a needexists for accurately positioning the distal locking screws and aligningthe drill for the drilling of the distal screw holes. Still further, aneed exists for an improved system for targeting landmarks whereby thecomponents may be easily sterilized or autoclaved and reused again.

SUMMARY

In a general aspect, a system for identifying a landmark includes afield generator for generating an electromagnetic field and a landmarkidentifier. The field generator and the landmark identifier are disposedin a common housing, and the field generator, the landmark identifier,and the common housing are autoclavable. The system also includes anorthopaedic implant located within the electromagnetic field, and theorthopaedic implant includes at least one landmark. A first magneticsensor is spaced apart from the at least one landmark by a set distance,and a processor compares sensor data from the first sensor and landmarkidentifier and uses the set distance to calculate the position of thelandmark identifier relative to the at least one landmark.

Implementations may include one or more of the following features. Forexample, the landmark is selected from the group consisting of astructure, a hole, a void, a boss, a channel, a detent, a flange, agroove, a member, a partition, a step, an aperture, a bore, a cavity, adimple, a duct, a gap, a notch, an orifice, a passage, a slit and aslot. The orthopaedic implant may be an intramedullary nail. Theorthopaedic implant has an outer surface and an inner surface forming acannulation, and the first sensor is mounted to a distal portion of aprobe that extends into the cannulation. The common housing in someimplementations also accommodates a drill motor, the drill motor beingcoupleable to a drill bit. The housing may include a drill sleeve. Thehousing may be disk-shaped. The drill extends normally outward from thedisk-shaped housing. The system can also include an insertion handleremovably coupled to the orthopaedic implant. An adjustable stop can becoupled to the implant and includes a slot through which the probeextends. The adjustable stop includes a clamp mechanism to hold theprobe in a fixed position. The probe may include a plurality of spacedapart markings, and the adjustable stop includes a clamp mechanism tohold the probe in a fixed position on a marking or between two markings.

In another general aspect, identifying a landmark includes providing anorthopaedic implant assembly having an orthopaedic implant having atleast one landmark, implanting the orthopaedic implant assembly in apatient, and placing a probe in the implant. The probe includes anelectromagnetic sensor. Identifying the landmark further includesgenerating an electromagnetic field that encompasses the sensor andlandmark, identifying the at least one landmark using a landmarkidentifier, installing a transfixion element in the at least onelandmark, and removing the probe. The landmark identifier is disposed inan autoclavable housing.

Implementations may include one or more of the following features. Forexample, the landmark is selected from the group consisting of astructure, a hole, a void, a boss, a channel, a detent, a flange, agroove, a member, a partition, a step, an aperture, a bore, a cavity, adimple, a duct, a gap, a notch, an orifice, a passage, a slit and aslot. The orthopaedic implant may be an intramedullary nail. Theorthopaedic implant has an outer surface and an inner surface forming acannulation, and identifying a landmark further includes mounting thefirst sensor to a distal portion of a probe that extends into thecannulation. The field generator and landmark identifier are disposed ina common autoclavable housing and identifying the landmark also includesautoclaving the housing. The field generator and landmark identifier aredisposed in a common autoclavable housing that may also accommodates adrill motor, the drill motor being coupled to a drill bit, andidentifying a landmark further comprises autoclaving the housing anddrill. The housing may include a drill sleeve. The housing may bedisk-shaped. Identifying a landmark also includes removably coupling aninsertion handle to the orthopaedic implant and/or clamping the probe ina fixed position. The probe comprises a plurality of spaced apartmarkings and the probe is clamped in a fixed position on a marking orbetween two markings.

In another general aspect, a system for identifying a landmark includesan autoclavable housing accommodating a field generator for generatingan electromagnetic field, a landmark identifier, and a drill motor. Anorthopaedic implant is located within the electromagnetic field and theorthopaedic implant has at least one landmark. A probe includes a firstelectromagnetic sensor and is placed within the orthopaedic implant andspaced apart from the at least one landmark by a set distance. Aprocessor is also included for comparing sensor data from the firstsensor and landmark identifier and for using the set distance tocalculate the position of the landmark identifier relative to the atleast one landmark. The first electromagnetic sensor is coupled to theprocessor via the probe.

In another general aspect, a kit for identifying landmarks on medicalimplants includes an autoclavable housing accommodating a fieldgenerator for generating an electromagnetic field, and a landmarkidentifier. A plurality of orthopaedic implants are also included, oneof which is located within the electromagnetic field. Each orthopaedicimplant includes at least one landmark. A plurality of probes, eachincluding an electromagnetic sensor, is included. One of the probesselected based on a size of the implant disposed in the electromagneticfield. The selected probe is placed within the implant in theelectromagnetic field and spaced apart from the at least one landmark bya set distance. A processor is included for comparing sensor data fromthe first sensor and landmark identifier and for using the set distanceto calculate the position of the landmark identifier relative to the atleast one landmark, wherein the first electromagnetic sensor is coupledto the processor via the probe.

In another general aspect, a system for targeting a landmark of anorthopaedic implant includes an autoclavable housing, a field generatordisposed within the housing for generating an electromagnetic field, afirst electromagnetic sensor for disposition at a set distance from thelandmark that generates sensor data in response to the generatedelectromagnetic field, and an element removably coupled to the housing,the element defining a longitudinal axis that represents one axis of thegenerated magnetic field. The system is configured to use the one axisof the generated electromagnetic field to determine the position of theelement relative to the landmark. Optionally, if the longitudinal axisof the element is offset from the axis of the field, one can compensatethis offset within the software.

Implementations may include one or more of the following features. Forexample, the system can include a first probe having a proximal portionand a distal portion, the first electromagnetic sensor disposed on thedistal portion of the probe, a retractable probe including the firstelectromagnetic sensor, or a retractable probe including the firstelectromagnetic sensor and a housing containing at least a portion ofthe retractable probe. A second electromagnetic sensor disposed on theproximal portion of the first probe can also be included. The system caninclude a second probe having a proximal and a distal portion and athird electromagnetic sensor disposed on the distal end of the secondprobe, where the second probe is longer than the first probe. The systemcan also include a processor for comparing the sensor data from thefirst electromagnetic sensor and the element and using the set distanceto calculate the position of the element relative to the landmark. Thesystem can include an adjustable stop that is connectable to theorthopedic implant. The adjustable stop can include a slot through whichthe first or the second probe extends and includes a clamping mechanismto hold the first or second probe in a fixed position. The first or thesecond probe can include a plurality of spaced apart indicators suchthat the clamping mechanism can be selectively set to hold the first orsecond probe in a fixed position at an indicator or between indicators.A handle can be removably coupled to the orthopedic implant. Theautoclavable housing can be disk-shaped. The element can include one ofa drill guide, a drill sleeve, a drill, a drill nose, a drill barrel, adrill chuck, and a fixation element. The orthopedic implant can includeone of an intramedullary nail, a bone plate, a hip prosthetic, a kneeprosthetic, a spinal prosthetic, and a shoulder prosthetic. The first orthe second probe can be coiled or bent prior to placement into theorthopedic implant. The first electromagnetic sensor includes a proximalend and a distal end. The distal end of the first electromagnetic sensoris connected to a proximal end of the orthopedic implant such that thefirst electromagnetic sensor is spaced apart a set distance from atleast one landmark disposed in a proximal region of the orthopedicimplant. At least the housing and the element are reusable. The housingis made from one of ceramic, silicone, polypropylene (PP), polycarbonate(PC), polymethylpentene (PMP), PTFE resin, or polymethyl methacrylate(PMMA or acrylic).

In another general aspect, a method includes exposing a landmarkidentifier to a sterilization process, the landmark identifiercomprising a mounting structure comprising elements that are configuredto receive induction coils of an electromagnetic field generator. Theelements are disposed on the mounting structure at locations andorientations relative to each other. Exposing the landmark identifier tothe sterilization process does not substantially alter the locations andorientations of the plurality of elements relative to each other.

Implementations may include one or more of the following features. Forexample, the method further includes using the landmark identifier totarget a landmark of an orthopaedic implant. Targeting may includeplacing the field generator within an operating range of a sensor andusing a display of a targeting system for positioning the landmarkidentifier in a predetermined position relative to the landmark.

In another general aspect, a method of making a landmark identifierincludes forming elements at locations in a mounting structure, securingelectromagnetic induction coils at orientations in the elements, forminga hole through the mounting structure, securing a coupling member to themounting structure, covering the mounting structure and theelectromagnetic induction coils with a third autoclavable material, and,optionally, applying a fourth autoclavable material over an exteriorsurface of the third autoclavable material. The mounting structurecomprises a first dimension stable autoclavable material. The couplingmember has a through hole that is aligned with the hole formed throughthe mounting structure when the coupling member is secured to themounting structure and the coupling member comprising a second dimensionstable autoclavable material. The third and fourth autoclavablematerials may also be dimension-stable materials.

Implementations may include one or more of the following features. Forexample, at least one of a sleeve or sleeve attachment is removablycoupled to the coupling member. The sleeve/sleeve attachment ispreferably made of dimension-stable autoclavable materials withsufficient strength. The method also includes forming one or moreapertures in the mounting structure and disposing at least one of ahollow material and a foam material, preferably closed cell foam, in theone or more apertures. A gripping surface is formed on an externalsurface of the landmark identifier and the gripping surface includes atleast one of a surface texture and a surface depression.

In another general aspect, an apparatus for targeting a landmark of anorthopaedic implant includes an insertion handle removably attachable tothe orthopaedic implant, an adjustable stop comprising an actuator, anda probe comprising a sensor and a plurality of markings to assist inplacing the probe and sensor at a desired location with respect to theorthopaedic implant.

Implementations may include one or more of the following features. Forexample, the adjustable stop includes a mating portion such that whenthe stop is connected to the insertion handle, the stop is located orfixed within three degrees of freedom. The insertion handle is attachedto the orthopaedic implant through use of a cannulated bolt.

In another general aspect, a kit for targeting a landmark of anorthopaedic implant includes a proximal targeting probe comprising atape body and a sensor included within or on the tape body at apredetermined distance from a reference point of the tape body. Theproximal targeting probe includes a first indicator that indicates thatthe proximal targeting probe is to be used for targeting proximallandmarks of an orthopaedic implant. The kit also includes a distaltargeting probe that includes a tape body that is longer than the tapebody of the proximal targeting probe and a sensor included within or onthe tape body of the distal targeting probe at a second predetermineddistance from a second reference point of the target body of the distaltargeting probe. The distal targeting probe includes a second indicatorthat indicates that the distal targeting probe is to be used fortargeting distal landmarks of the orthopaedic implant.

Implementations may include one or more of the following features. Forexample, the first indicator includes a color-coded grip and the secondindicator includes a color-coded grip that is a different color than thefirst indicator. The first indicator includes a color-coded grip and thesecond indicator includes a color-coded grip that is a different colorthan the first indicator. The proximal targeting probe includes a cablefor carrying a signal from the sensor included within or on the tapebody of the proximal targeting probe to a control unit, and the distaltargeting probe includes a second cable for carrying a second signalfrom the sensor included within or on the tape body of the distaltargeting probe to the control unit. The sensors included within or onthe tape bodies of the proximal and distal targeting probes areconnected to one or more Programmable Read-Only Memory microchip thatidentifies whether the proximal and distal targeting probes are used forproximal or distal targeting. The tape bodies of the proximal and distaltargeting probes include one or more bends to bias at least a portion ofthe tape bodies against a wall of the orthopaedic implant.

In another general aspect, a probe for use in targeting a landmark of anorthopaedic implant includes a housing, a retractable or extensible bodydisposed within the housing. The body is configured to form a generallystraight shape when extended from the housing. A sensor is disposedwithin the body and is positionable at a first location for targeting aproximal landmark of the orthopaedic implant. The sensor is positionableat a second location for targeting a distal landmark of the orthopaedicimplant. The body comprises one of layered, flexible stainless steelspring bands, resilient plastics, or rubber tubing or sheeting. The bodyincludes a plurality of nested segments of tubing that can extend andretract by sliding within adjacent tubing segments.

In another general aspect, an apparatus for targeting a landmark locatedin a proximal end of an orthopaedic implant includes an insertion handleand a sensor disposed within or on the insertion handle at apredetermined distance from a proximal locking aperture formed in theorthopaedic implant when the insertion handle is attached to theorthopaedic implant. The sensor is passive or electrically powered. Thesensor is mounted in a housing that is unitary or integral with theinsertion handle.

In another general aspect, a landmark identifier for use in a surgicaltargeting system includes a mounting structure that has elements thatare configured to receive induction coils of an electromagnetic fieldgenerator. The elements are disposed on the mounting structure atlocations and orientations relative to each other. The landmarkidentifier also includes at least one covering formed over the mountingstructure. In use, the locations and orientations of the elementsrelative to each other remain substantially unaltered after exposure toone or more sterilization processes.

Implementations may include one or more of the following features. Forexample, the mounting structure defines one or more openings and ahollow insert or a closed cell foam material is disposed in theopening(s). The field generator includes at least one of a sleeve andsleeve attachment having a longitudinal axis aligned with the center ofgravity of the landmark identifier. The mounting structure is formed ormolded from a dimension stable autoclavable material. The mountingstructure includes a reinforced epoxy laminate. The field generatorincludes electromagnetic induction coils mounted in the elements at thelocations and orientations relative to each other. The field generatorincludes at least one covering comprises a first covering formed from anautoclavable material and the first covering is disposed over each ofthe elements. The first covering comprises a silicone material. Thefield generator includes a coupling member attached or molded to themounting structure and configured to receive a removable sleeve orsleeve attachment, wherein the coupling member and the sleeve/sleeveattachment comprise dimension stable autoclave materials. The sleeve andthe sleeve attachment comprise a frustoconical portion.

In another general aspect, a method of locking an orthopaedic implanthaving at least one hole using an electromagnetic field generatorincludes aligning a drill guide tip, preferably a serrated tip, over theone hole of the orthopaedic implant using the electromagnetic fieldgenerator, making an incision into soft tissue, inserting the drillguide tip through the incision against the bone, pivoting the drillguide tip against the bone to align the axis of the drill guide with anaxis of the hole, and drilling through the bone. The method may furtherinclude engaging a fastener with the bone through the hole of theorthopaedic implant to lock the orthopaedic implant to the bone.Engaging the fastener with the bone includes removing a drill sleeve andsleeve attachment from the coupling member, coupling or inserting, adriver with a fastener through the coupling member, aligning an axis ofthe fastener and/or driver with the axis of the hole of the orthopaedicimplant, and driving the fastener into the hole to lock the orthopaedicimplant to the bone.

Implementations may include one or more of the following features. Forexample, the method may further include using an indicator coupled witha driver for inserting the fastener into bone at a desired depth. Theindicator includes a laser etching corresponding to the actual orcalculated dimension or height of a fastener head and a circumferentialgroove formed at the base of the head. The indicator is configured toindicate the position of the fastener head relative to a bone surface bythe relative location of a reference portion of the indicator and thecircumferential groove.

The disclosed methods and apparatuses include several advancements.First, the disclosed methods and apparatuses can operate independentlyof fluoroscopy and eliminate the necessity of X-ray devices fortargeting of transfixion elements, thereby reducing the exposure ofusers and patients to radiation. Second, disclosed methods andapparatuses allow a user to lock the driving-end of the implant beforelocking the non-driving end of the implant. In other words, thedisclosed methods and apparatuses do not require use of an implantcannulation that requires proximal locking prior to distal locking.

Other advantages and features will be apparent from the followingdetailed description when read in conjunction with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system for identifying a landmark.

FIG. 2 is a sectional view of an orthopaedic implant of FIG. 1.

FIG. 3 is a partial sectional of the implant of FIGS. 1 and 2illustrating the sensor mounting.

FIG. 4 is a partial sectional view of another sensor mounting in animplant.

FIG. 5 is a sectional view of the sensor and implant illustrated in FIG.4.

FIG. 6 illustrates another orthopaedic implant assembly.

FIG. 7 is a partial plan view of a removable lead.

FIG. 8 is a top view of the orthopaedic implant assembly illustrated inFIG. 6.

FIG. 9 illustrates a landmark identifier that includes a drill sleeve.

FIG. 10 is a partial and sectional view illustrating two point contactsof an implant.

FIG. 11 is another partial sectional view illustrating point contacts inanother implant.

FIG. 12A is a partial and sectional view of an implant illustrating acrimp electrical connection.

FIG. 12B is a partial exploded view illustrating the electricalconnection in a disclosed implant.

FIG. 12C is a side view of the electrical connection illustrated in FIG.12B.

FIG. 12D is a partial exploded illustrating the electrical connection inanother disclosed implant.

FIG. 13A is a partial perspective and exploded view illustratingalternative mechanisms for aligning a disclosed orthopaedic implant anda disclosed insertion handle.

FIG. 13B is a partial perspective and exploded view illustratingalternative mechanisms for aligning a disclosed orthopaedic implant andan electrical connection.

FIG. 14 is a partial side view illustrating a connection of theinsertion handle to the orthopaedic implant.

FIG. 15 illustrates another system for identifying a landmark.

FIG. 16 is a schematic illustration of view selection criteria.

FIG. 17 is a flowchart illustrating view selection during a fixationsurgery.

FIG. 18 is a schematic illustration of another method of aligning alandmark identifier.

FIG. 19 is a schematic illustration of another disclosed method ofaligning a landmark identifier.

FIG. 20 illustrates a disclosed monitor with exemplary views.

FIG. 21 illustrates another disclosed landmark identifier.

FIG. 22 is a partial view another disclosed insertion handle.

FIG. 23 illustrates another disclosed system for identifying a landmark.

FIG. 24 is a partial view of yet another disclosed insertion handle.

FIG. 25 illustrates another disclosed system for identifying a landmark.

FIG. 26 is a partial cross-sectional view of an intramedullary nail.

FIG. 27 illustrates a packaging for a disclosed implant.

FIG. 28 illustrates a method of connecting a landmark identifier systemto a network.

FIG. 29 illustrates yet another disclosed system for identifying alandmark.

FIG. 30 is a flow chart for using a disclosed landmark identifyingsystem.

FIG. 31 is another flow chart for using a disclosed landmark identifyingsystem.

FIG. 32 is a schematic illustration of tracking drill depth.

FIGS. 33A and 33B are also schematic illustrations of tracking drilldepth.

FIG. 34 is a partial illustration of a disclosed device for trackingdrill depth.

FIG. 35 is a perspective view of another insertion handle.

FIG. 36 is a top perspective view of an adjustable stop.

FIG. 37 is a bottom perspective view of the adjustable stop illustratedin FIG. 36.

FIG. 38 is another illustrating system calibration.

FIG. 39 is a perspective view of another landmark identifier housing afield generator and a drill sleeve and that may be sterilized or subjectto an autoclave procedure.

FIG. 39a is a top perspective view of a mounting structure.

FIG. 39b is a perspective view of a drill sleeve attachment and drillsleeve.

FIG. 40 is a side view of the landmark identifier/field generator/drillsleeve of FIG. 39 making contact with a bone.

FIG. 41 is a perspective view of the landmark identifier/fieldgenerator/autoclavable housing of FIG. 39 coupled to a screw driverattachment.

FIG. 42 is a plan view of an insertion handle, adjustable stop andprobe.

FIG. 43 is a perspective view of an exemplary adjustable stop to hold aprobe in a desired position.

FIG. 44 is a perspective view of another exemplary adjustable stop.

FIG. 45 is a perspective view of an intramedullary nail, an insertionhandle, an adjustable stop, and a probe.

FIG. 46 is a perspective view of another intramedullary nail, aninsertion handle, an adjustable stop, and a probe.

FIG. 47 is a perspective view of two probes for use in targetinglandmarks of an implant.

FIG. 48 is a perspective view of another probe for use in targetinglandmarks of an implant.

FIG. 49 is a sectional view of a retractable probe.

FIG. 50 is a perspective view of an intramedullary, an insertion handle,and an adjustable stop.

FIG. 51 is an illustration of a system for targeting a landmark of animplant.

FIG. 52 is an illustration of a device for use in calibrating the systemof FIG. 51.

FIGS. 53-62 are illustrations of adjustable stops.

It should be understood that the drawings are not necessarily to scaleand that the disclosed implementations are sometimes illustrateddiagrammatically and in partial views. In certain instances, detailswhich are not necessary for an understanding of the disclosure or whichrender other details difficult to perceive may have been omitted. Itshould be understood, of course, that this disclosure is not limited tothe particular implementations illustrated herein.

DETAILED DESCRIPTION

Referring to the accompanying drawings in which like reference numbersindicate like elements, FIG. 1 illustrates one disclosed system 10 foridentifying a landmark. The system 10 may include a processor 12, amagnetic field generator 16, a landmark identifier 18, and anorthopaedic implant assembly 28. The system 10 may also include amonitor 14 electrically connected to the processor 12 and an insertionhandle 40 removably attached to the orthopaedic implant assembly 28. Theprocessor 12 is depicted as a desktop computer in FIG. 1 but other typesof computing devices may be used. As examples, the processor 12 may be adesktop computer, a laptop computer, a personal data assistant (PDA), amobile handheld device, or a dedicated device. The magnetic fieldgenerator 16 is a device available from Ascension Technology Corporationof 107 Catamount Drive, Milton Vt., U.S.A.; Northern Digital Inc. of 103Randall Drive, Waterloo, Ontario, Canada; or Polhemus of 40 HerculesDrive, Colchester Vt., U.S.A. Of course, other generators may be used.As examples, the field generator 16 may provide a pulsed direct currentelectromagnetic field or an alternating current electromagnetic field.The system 10 may also include a control unit (not shown) connected tothe magnetic field generator 16. The control unit controls the fieldgenerator 16, receives signals from small mobile inductive sensors, andcommunicates with the processor 12, either by wire or wirelessly. Thecontrol unit may be incorporated into the processor 12 either throughhardware or software.

The system 10 is a magnetic position tracking system. For illustrativepurposes, the system 10 may include a magnetic field generator 16comprised of suitably arranged electromagnetic inductive coils thatserve as the spatial magnetic reference frame (i.e., X, Y, Z). Thesystem 10 may also include small mobile inductive sensors, which areattached to the object being tracked. It should be understood that othervariants could be easily accommodated. The position and angularorientation of the small mobile inductive sensors are determined fromits magnetic coupling to the source field produced by magnetic fieldgenerator 16.

It is noted that the magnetic field generator 16 generates a sequence,or set, of here six, different spatial magnetic field shapes, ordistributions, each of which is sensed by the small mobile inductivesensors. Each sequence enables a sequence of signals to be produced bythe small mobile inductive sensors. Processing of the sequence ofsignals enables determination of position and/or orientation of thesmall mobile inductive sensors, and hence the position of the object towhich the small mobile inductive sensor is mounted relative the magneticcoordinate reference frame which is in fixed relationship to themagnetic field generator 16. The processor 12 or the control unit mayuse the reference coordinate system and the sensed data to create atransformation matrix comprising position and orientation information.

The landmark identifier 18 is used to target a landmark, such as alandmark on the orthopaedic implant assembly 28. The landmark identifier18 may include one or more small mobile inductive sensors or may includethe field generator. The landmark identifier 18 has a second sensor 20.The landmark identifier 18 may be any number of devices. As examples,the landmark identifier may be a device that includes a structure thatprovides a user with an understanding of the location and orientation ofa hidden landmark. For example, the landmark identifier can include adrill guide, a drill sleeve, a drill, a drill nose, a drill barrel, adrill chuck, or a fixation element. In some implementations, thestructure can be a housing having an opening, or other structure thatindicates the location and orientation of a landmark. In FIG. 1, thelandmark identifier 18 is a drill sleeve and includes a sensor 20,whereas in FIG. 39, the landmark identifier 2016 includes a housing 2020having a central aperture and includes a magnetic field generator (notshown) in the housing 2020. The landmark identifier 18 may include oneor more of a serrated tip 22, a tube 24, and a handle 26. The tube 24also may be referred to as a bushing, cylinder, guide, or drilling/screwplacement guide. The second sensor 20 is oriented relative to an axis ofthe tube 24. The tube 24 may receive a drill. This offset of the sensor20 from the tube 24 allows the position and orientation of the tube tobe located in space in six dimensions (three translational and threeangular) relative to the magnetic field generator 16 and/or anothersensor in the system. The processor 12 may need to be calibrated toadjust for the offset distance of the second sensor 20. The landmarkidentifier 18 and the field generator 16 may be combined into a singlecomponent. For example, the field generator 16 may be incorporatedwithin the handle 26.

The orthopaedic implant assembly 28 may include an implant 30 and one ormore small mobile inductive sensors. The orthopaedic implant assembly 28includes a first sensor 32. In FIG. 1, the implant 30 is in the form ofintramedullary nail but other types of implants may be used. Asexamples, the implant may be an intramedullary nail, a bone plate, ashoulder prosthetic, a hip prosthetic, or a knee prosthetic. The firstsensor 32 is oriented and in a predetermined position relative to one ormore landmarks on the implant 30. As examples, the landmark may be astructure, a void, a boss, a channel, a detent, a flange, a groove, amember, a partition, a step, an aperture, a bore, a cavity, a dimple, aduct, a gap, a notch, an orifice, a passage, a slit, a hole, or a slot.In FIG. 1, the landmarks are transfixion holes 31. The offset of thefirst sensor 32 from the landmark allows the position of the landmark tobe located in space in six dimensions (three translational and threeangular) relative to the magnetic field generator 16 or another sensorin the system, such as the second sensor 32. The processor may need tobe calibrated to adjust for the offset distance of the first sensor 32.

The first sensor 32 and the second sensor 20 are coupled to theprocessor 12. This may be accomplished by wire or wirelessly. The firstsensor 32 and the second sensor 20 may be a six degree of freedom sensorconfigured to describe the location of each sensor in threetranslational axes, generally called X, Y and Z and three angularorientations, generally called pitch, yaw and roll. By locating thesensor in these reference frames, and knowing the location andorientation of each sensor, the landmark identifier 18 may be locatedrelative to the landmark on the implant 30. In one particularimplementation, the information from the sensors allows for a surgeon toplan the surgical path for fixation and properly align a drill with ablind fixation hole 31. The sensors 32, 20 are six degrees of freedomsensor from Ascension Technology Corporation of 107 Catamount Drive,Milton Vt., U.S.A.; Northern Digital Inc. of 103 Randall Drive,Waterloo, Ontario, Canada; or Polhemus of 40 Hercules Drive, ColchesterVt., U.S.A. Of course, other sensors may be used.

The first sensor 32 may be attached to the implant 30. For example, thefirst sensor 32 may be attached to an outer surface 37. In FIG. 1, theimplant 30 may also include a groove 34 and a pocket 36 (best seen inFIG. 2). The groove 34 and pocket 36 are located in a wall of theimplant 30. The first sensor 32 is intended to be attached to theimplant 30 and installed in a patient for the service life of theimplant 30. Further, the orthopaedic implant assembly 28 may include acover 38 to cover the pocket 36 and/or the groove 34. The cover 38 maybe substantially flush with the external surface 37 of the implant 30.Accordingly, the implant 30 may include a second opening 39 (see FIG. 2)to receive the cover 38.

The first sensor 32 may be tethered to leads for communication andpower. The leads, and the sensor, may be fixed to the implant 30. A lead50 may be used to connect the first sensor 32 to the processor 12 or thecontrol unit. The lead 50 may be made from biocompatible wire. As anexample, the lead 50 may be made of DFT wire available from Fort WayneMetals Research Products Corp., 9609 Indianapolis Road, Fort Wayne, Ind.46809. DFT is a registered trademark of Fort Wayne Metals ResearchProducts Corp. A first connector 52 may be used to place the lead 50relative to the implant 30. A second connector 54 may be used to connectthe lead 50 to another device, such as the processor 12, the controlunit, or the insertion handle 40.

The first sensor 32 may be fixed in the pocket 36 using a range of highstiffness adhesives or polymers including epoxy resins, polyurethanes,polymethyl methacrylate, polyetheretherketone, UV curable adhesives,silicone, and medical grade cyanoacrylates. As an example, EPO-TEK 301available from Epoxy Technology, 14 Fortune Drive, Billerica, Mass.01821 may be used. The lead 50 may be fixed in the groove in a similarmanner. These types of fixation methods do not adversely affect theperformance of the electrical components. Thereafter, the cover 38 maybe placed on the implant 30 and welded in-place. For example, the coversmay be laser welded to the implant.

The monitor 14 may be configured to display the position and orientationof the first sensor 32 and the second sensor 20 so that the display mayshow a surgeon both sensor positions and orientations relative to oneanother. The processor 12 may send positional data, either by wire orwirelessly, to a user interface, which may graphically display therelative positions of the landmark identifier and the implant on themonitor. The view displayed on the monitor 14 may be oriented relativeto the landmark identifier so that the surgeon may visualize the userinterface as an extension of the landmark identifier. The user interfacealso may be oriented so that the surgeon may view the monitorsimultaneously with the surgical field.

The insertion handle 40 may be used for installation of the orthopaedicimplant assembly 28 and also may be used to route the leads from thefirst sensor 32. For example, the insertion handle 40 may route bothcommunication and power leads between the implant 30 and the processor12.

In FIG. 1, the landmark identifier 18 and the insertion handle 40 eachinclude a communications module 21, 25 for wirelessly transmitting datafrom the sensor 20, 32 to the processor 12, but those skilled in the artwould understand that other methods, such as by wire, may be used. Thesecond connector 54 plugs into the communications module 25.Alternatively, and as is explained in greater detail below, the implant30 and the insertion handle 40 may have mating electrical contacts thatform a connection when the components are assembled such that the firstsensor 32 is connected to the communications module 25.

The implant 30 may include a communications circuit and an antenna forwireless communication. Power for the first sensor 32 and/or thecommunications circuit may be positioned within the insertion handle 40.For example, a battery may be placed within the insertion handle 40 fortransferring power to the first sensor 32 and/or other electronics.Alternatively, the communications circuit, the antenna, and the batterymay be located within the insertion handle 40 and each of these may betethered to the first sensor 32. In yet another implementation, theimplant 30 may include a coil to inductively power the communicationscircuit and communicate data from the first sensor 32. The power sourcemay be a single source mode or may be a dual mode AC/DC.

In use, the orthopaedic implant assembly 28 is installed in a patient.For example, in the case of internal fixation, the intramedullary nailis placed within an intramedullary canal. Optionally, the user may usetransfixion elements, such as screws, to first lock the proximal end ofthe intramedullary nail. An operator uses the targeting device 18 andthe first sensor 32 to identify the landmarks. For example, in the caseof intramedullary nail fixation, a surgeon uses the targeting device 18to identify the blind transfixion holes 31 and drill through the holes31 for placement of a transfixion element.

FIG. 2 further illustrates the implant 30 as illustrated in FIG. 1. Theimplant 30 may include the first sensor 32, the longitudinal groove 34,the pocket 36, the cover 38, and the second opening 39. As examples, thecover 38 may be comprised of gold or titanium foil. The implant 30 mayinclude an inner surface 35 that forms a cannulation 33. The outersurface of the implant 30 is shown at 37.

FIG. 3 illustrates an implementation of the first sensor 32. The firstsensor 32 may include two coils cross-layered to one another and havingan angle α.

FIGS. 4 and 5 illustrate another implementation of the first sensor 32.The first sensor may include two coils generally orthogonal to oneanother in order to establish the orientation and position in the sixdegrees of freedom. A first coil may be oriented along the length of theimplant 30. The second coil may be oriented either wrapped around thecircumference of the implant, for example in a groove, or along theradius of the implant 30. In addition, while the coils may beperpendicular to one another, other orientations may be used, althoughthe mathematics may be more complex. Further, the coils may be orientedspirally around the implant 30. Such an orientation may allow two coilsto be placed perpendicular to each other with both coils placed alongboth the length of the implant and along the circumference of theimplant 30.

FIGS. 6-8 illustrate a second implementation of the orthopaedic implantassembly 60. The orthopaedic implant assembly 60 may include the implant30. In FIG. 6, the implant 30 includes landmarks in the form oftransfixion holes 31. The implant 30 may include a longitudinal internalgroove 66 and a removable lead 64. In FIG. 8, a diameter of thelongitudinal groove 66 is shown as intersecting with the cannulation 33;however, in other implementations, the diameter of the longitudinalinternal groove is contained between the outer surface 37 and the innersurface 35. The removable lead 64 may include the first sensor 32 at itsdistal end portion 65. The first sensor 32 is located a known offsetfrom the landmarks 31. The implant in FIGS. 6-8 is comprised ofbiocompatible material, and may be a metal alloy or a polymer. Thelongitudinal groove 66 may be machined or molded in place.

In use, the implant 30 with the removable lead is installed in apatient. For example, in the case of internal fixation, theintramedullary nail is placed within an intramedullary canal.Optionally, the user may use transfixion elements, such as screws, tofirst lock the proximal end of the intramedullary nail. Because of thelocation of the longitudinal groove 66, the removable lead 64 does notinterfere with locking the proximal end of the intramedullary nail. Anoperator uses the targeting device 18 and the first sensor 32 toidentify the landmarks 31. For example, in the case of intramedullarynail fixation, a surgeon uses the targeting device 18 to identify theblind transfixion holes 31 and drill through the holes 31 for placementof a transfixion element. After the implant 30 is secured, the operatorremoves the removable lead 64 and it may be discarded.

A method for identifying a landmark is disclosed. The method may includeproviding an orthopaedic implant assembly having an orthopaedic implantwith a longitudinal groove and a removable lead or probe having anelectromagnetic sensor attached thereto situated within the longitudinalgroove. The orthopaedic implant includes a proximal end portion, adistal end portion, and at least one landmark on the distal end portion.The method includes implanting the orthopaedic implant assembly in apatient. Then, transfixion elements in the proximal end portion areinstalled. At least one distal landmark is identified using a landmarkidentifier. A transfixion element is installed in the at least onedistal landmark. The removable lead or probe may then be removed. Thesituation of the removable lead or probe within the longitudinal grooveallows for proximal locking of the implant prior to distal locking.

FIG. 9 illustrates the landmark identifier 18 of FIG. 1. The landmarkidentifier 18 may include the sensor 20, the serrated tip 22, the tube24, and the handle 26. A drill 90 has markings 92 that interact with amarking sensor 19 adjacent the tube 24. The interaction is similar to apair of digital measuring calipers in that the position between themarkings 92 and the sensor 19 equate to a distance. This distance can beused to determine the depth of the drill into the bone and ultimatelythe length of the bone screw that will be inserted into the drilledhole. Distance, or drill depth, readings are only obtainable when themarkings 92 and the sensor 19 are in close proximity to each other, i.e.the drill 90 is inside the tube 24. Exemplary measurement devices areillustrated in U.S. Pat. Nos. 6,675,491 and 7,253,611. The markingsensor 19 is connected to the communications module 21. Alternatively,the marking sensor 19 may be connected by wire to the processor 12. InFIG. 9, the communications module 21 may include a third connector 23for electrical connection to the processor 12.

FIGS. 10-12 illustrate exemplary methods of electrically connecting theimplant 30 to the insertion handle 40, which has correspondingelectrical contacts. In FIG. 10, biasing elements 72 bias contacts 70toward the insertion handle 40. In FIG. 11, the implant 30 haselastomeric electrical contacts 74. In FIG. 12A, wires extending betweenthe lead 50 and another component are crimped together at junction 76.In one method, the wires are torn free and separated at the junction 76after installation of the orthopaedic implant assembly 28. In yetanother method, the wires are cut above the junction 76 afterinstallation of the orthopaedic implant assembly 28. In FIGS. 12 B andC, two flex boards 53 are soldered together one or more pads 57 toconnect a wiring harness 55 to the sensor. The wire harness 55 may bemounted to the insertion handle 40 or within a cannulation of theinsertion handle 40. In the depicted implementation, four pads 57 aresoldered together. Locking tabs 59 are sandwiched between the implant 30and the insertion handle 40 to withstand abrasion and tension associatedwith the implant insertion. Once the insertion handle 40 is removed, thewire harness 55 can be pulled such that all non-biocompatible materialsare pulled with it. In FIG. 12D, rings 61, 63 are connected duringmanufacturing. After implantation, both rings 61, 63 are removed bypulling on a jacketed wire 67.

Referring now to FIGS. 13A and 13B, the implant 30 and/or the insertionhandle 40 may include one or more alignment features 44 and mating notch80 or alignment pin 46 and mating hole 82. The insertion handle may beconfigured to align with an upper surface of the implant. In oneimplementation, the insertion handle may have a key configured to mateto a slot on the implant. Other alignment guides may be used. Inaddition, the guide may have an electrical connector configured to mateto an electrical connector on the implant. The connection between theguide and the implant may be spring loaded to ensure electrical contactbetween the electrical connectors. In order to avoid shorting theconnection between the guide and the implant, the electrical connectormay be insulated. As another example of electrically connecting theinsertion handle to the implant, the electrical connectors may include apost and slip rings. The rings may be located on the implant, and theposts located on the insertion handle. The posts are biased to contactthe rings. In such an implementation, the angular location of theinsertion handle 40 relative to the axis of the implant is not fixed.This would allow the insertion handle 40 to be positioned to the implantirrespective of angular position.

In another implementation shown in FIG. 13B, the implant 30 and/or theinsertion handle 40 may include one or more alignment pin 47 and matinghole 83. The alignment pins 47 may be spear tip pins designed to engagea single time and when removed, the pins grip portion of the implant toremove all non-biocompatible materials with them.

Any of the electrical connectors above may include a memory storagedevice (not shown) for storing offset values for sensor calibration.

Referring now to FIG. 14, the implant 30 and the insertion handle 40 maybe sized such that space remains available for the first connector 52even when the components are assembled or mated. As an example, thesystem for identifying a landmark may be used to target blind screwholes of an implanted intramedullary nail. The intramedullary nail isimplanted in the patient. The electromagnetic field generator isactivated. The processor receives signals from the sensor mounted to theintramedullary nail and from the sensor mounted to the landmarkidentifier, such as a drill sleeve. A computer program running on theprocessor uses the information of the at least two sensors andgraphically display them in relative position on the monitor. A surgeonmoves the landmark identifiers into position using feedback provided bythe processor. When the landmark identifier is in the proper location,the surgeon drill through bone and the intramedullary nail to create ascrew hole. The processor may provide feedback as to the depth of thedrilled hole. The surgeon may then place a screw through the drilledhole to affix the blind hole of the intramedullary nail.

Provided feedback information may be selected from the group consistingof audible, visual, and tactile. The audible feedback may be outputthrough a speaker, headphones, ear buds, or an ear piece. The audiblefeedback signal may be transmitted over wire or wirelessly using radiofrequency or terrestrial data transmission. The visual feedback may beoutput through a cathode ray tube, a liquid crystal display, or a plasmadisplay. Visual feedback devices may include, as examples, a televisionmonitor, a personal digital assistant, or a personal media player. Thevisual feedback signal may be transmitted over wire or wirelessly usingradio frequency or terrestrial data transmission. The tactile feedbackmay be output through gloves, instruments, or a floor mat. The tactilefeedback signal may be transmitted over wire or wirelessly using radiofrequency or terrestrial data transmission.

FIG. 15 illustrates a system 110 for identifying a landmark in anotherimplementation. The system 110 may include a processor 112, a landmarkidentifier 118, and an orthopaedic implant assembly 128. The system 110may also include a monitor 114 and an insertion handle 140.

The landmark identifier 118 is used to target a landmark. The landmarkidentifier 118 may include a second sensor 120. In FIG. 15, the landmarkidentifier 118 is a drill sleeve with a serrated tip 122, a tube 124,and a handle 126. The second sensor 120 is oriented relative to an axisof the tube, which may receive a drill. This offset of the sensor fromthe tube allows the position of the tube to be located in space in sixdimensions (three translational and three angular) relative to thetransmitter or another sensor in the system. The processor may need tobe calibrated to adjust for the offset distance of the second sensor120.

The orthopaedic implant assembly 128 may include an implant 130 and amagnet 132.

The magnet may be a permanent magnet or an electromagnet. The magnet 132is oriented in a predetermined position relative to a landmark on theorthopaedic implant 130. This offset of the magnet from the landmarkallows the position of the landmark to be located in space in sixdimensions (three translational and three angular) relative to thetransmitter or another sensor in the system, such as the second sensor.The processor may need to be calibrated to adjust for the offsetdistance of the magnet 132. As with the implant 30 of FIG. 1, theimplant 130 may also include a pocket 136 and a cover 138. In the caseof an electromagnet, a lead 150 connects to the magnet 132 and iscontained within a groove 134.

As an example, the system for identifying a landmark may be used totarget blind screw holes of an implanted intramedullary nail. Theintramedullary nail is implanted in the patient. The processor receivessignals from the sensor mounted to the landmark identifier, such as adrill sleeve. A computer program running on the processor uses theinformation of the sensor and graphically displays the sensor inrelative position to the magnet on the monitor. A surgeon moves thelandmark identifiers into position using feedback provided by theprocessor. When the landmark identifier is in the proper location, thesurgeon drill through bone and the intramedullary nail to create a screwhole. The processor may provide feedback as to the depth of the drilledhole. The surgeon may then place a screw through the drilled hole toaffix the blind hole of the intramedullary nail.

FIG. 16 illustrates a method for selecting views corresponding tolandmark identifier position. The view displayed on the monitor isdependent upon the location of the landmark identifier relative to theimplant. The diameter of the implant is broken into sectors or fields.In FIG. 16, the diameter is broken down into three fields: (A) 135° to225°; (B) 0° to 135°; and (C) 225° to 360°. The initial view is basedupon landmark identifier orientation relative to the implant. As theuser moves landmark identifier toward or away from the implant, themonitor display zooms in or out on the selected field.

FIG. 17 is a flowchart for view selection and display of one landmark.The process may be repeated for multiple landmarks. The processor 12uses the transformation matrix in the following process steps. In step200, landmark identifier position is computed relative to the implantbased upon the positions of the relevant sensors, and the landmarkclosest the landmark identifier is selected for display. In step 210, aglobal view is defined showing the whole implant with the selectedlandmark oriented for proper viewing. A global view is analogous toviewing the implant at a distance. In step 220, there is a decisionwhether there are multiple landmarks having the same orientation. Ifyes, then in step 230, the processor calculates which landmark isnearest to the landmark identifier position and selects it for viewing.If no, in step 240, a local view is defined and centered upon theselected landmarks. A local view is analogous to viewing the implant inclose proximity. In some implementations, it may be desirable to hidethe landmark identifier when the local view is defined. In steps 250,260, and 270, the processor 12 identifies the distance from landmarkidentifier to the landmark and depending upon the decision made, eitherhides or renders the landmark identifier. In step 250, the distance fromlandmark identifier to the landmark and a comparison is made between thecalculated distance D and set variables T_(Global) and T_(Local). IfD>T_(Global), then the global view is selected in step 260 and theprocessor proceeds to step 285. If D<T_(Local), then the local view isselected and centered upon the landmark in step 270. Thereafter, theprocessor proceeds to step 275. In optional step 275, the landmarkidentifier is hidden. Otherwise, an intermediate camera position iscalculated based upon the distance D to enable a smooth transition fromglobal view to a local view in step 280. In step 285, the landmarkidentifier is shown. In step 290, the scene with selected cameraposition is rendered.

FIG. 18 is a schematic illustrating a first alternative method ofaligning the landmark identifier. A computer program running on theprocessor may be used to take the information of the at least twosensors and graphically display them in relative position (the secondsensor relative to the first sensor) on the monitor. This allows theuser to utilize the system to guide the placement of the landmarkidentifier. In the case of drilling a blind intramedullary nail hole,the system guides the user in placement of the drill sleeve andsubsequently drilling accurately thru the hole in the intramedullarynail. The graphical user interface may include an alignment guide foreach of the degrees of freedom. A minimum alignment level may be setsuch that the surgeon continues to orient the landmark identifier untileach of the degrees of freedom meets the minimum alignment level for aneffective placement of the landmark identifier. The example of FIG. 18shows an instance where the placement in the Y-direction meets theminimum required tracking placement. However, none of the othertranslational or rotational meets the minimum requirements. While themagnitudes of tracking are illustrated as bar graphs, other graphicalrepresentations, such as color coding, may be used.

FIG. 19 is a schematic illustrating a second alternative method ofaligning the landmark identifier. In this implementation, a graphicalinterface using a plurality of LEDs to position the drill may be placedupon the landmark identifier, such as a drill sleeve. By using the LEDsto trajectory track the drill, the surgeon may align the drill with theblind fixation hole. The trajectory may additionally use secondarydisplays to add more information to the system. For example, foraffecting the magnitude of adjustment, the trajectory may includeflashing LEDs so that high frequency flashing requires largeradjustments while low frequency flashing may require smalleradjustments. Similarly, colors may add information regarding adjustmentsto alignment.

FIG. 20 illustrates a monitor with exemplary views. A first portion 500indicates the distance the drill is on each side of the implant. Thismay provide the user with a better understanding of drill depth andalert the user when to stop when appropriate drill depth has beenachieved. The second portion 510 provides the user with alignmentinformation. As an example, drill depth data may be obtained using theimplementation illustrated in FIG. 9.

FIG. 21 illustrates an alternative implementation of the landmarkidentifier. The landmark identifier is configured to display, with LEDs,the position and trajectory information for proper alignment. The sizeof the LEDs may display additional information regarding the magnitudeof required adjustment. The trajectory light may display a simple on/offtoggle between an aligned trajectory and a mal-aligned trajectory. Asanother example, the trajectory LED may be color coded to suggest themagnitude of necessary adjustment for proper alignment.

FIG. 22 illustrates a first alternative implementation of the insertionhandle 700. The insertion handle 700 may include an arcuate slot 710.The arcuate slot limits the movement of the landmark identifier 18, 118within the operating space. In the case of identifying a blind screwhole, the arcuate slot limits the movement of the drill sleeve for fineadjustment of its position. The insertion handle 700 may include acarriage 712 that receives the landmark identifier and rides in the slot710.

FIG. 23 illustrates the system for identifying a landmark in a thirdimplementation. In this implementation, the orthopaedic implant 800 is abone plate and the insertion handle 810 is a little guide affixed to thebone plate. The inductive sensor is placed on the surface of theorthopaedic implant 800 relative to one or more landmarks. The guide 810may allow a landmark identifier 818 to translate and/or rotate relativeto the guide to properly align the landmark identifier with a landmark802, such as a fastener hole. In addition, where multiple fixation holesare on the implant, then additional guide holes 812 on the guide 810 mayhelp approximate the position of the additional fixation holes.

FIG. 24 illustrates a second alternative implementation of the insertionhandle. The insertion handle 900 may include fine adjustment in landmarkidentifier 918 positions through the use of small servomotors 920, 922,924. The servomotors 920, 922, 924 may adjust the orientation andposition of the landmark identifier 918. Control of the servos may beautomatic or may be controlled by a surgeon.

FIG. 25 illustrates a bone 100 and another system 1010 for identifying alandmark. The system 1010 may include a control unit 1012, a fieldgenerator 1014, a landmark identifier 1016, an intramedullary nail 1024,and a probe 1029. The landmark identifier 1016 also may be referred toas a targeter. The control unit 1012 may be included as part of theprocessor described above or may be a separate unit. The intramedullarynail 1024 is inserted into the bone 100, and the intramedullary nail1024 has a hole or landmark 1028. The field generator 1014 iselectrically connected to the control unit 1012. An insertion handle1022 is removably attached to the intramedullary nail 1024. Theinsertion handle 1022 and/or the intramedullary nail 1024 may be formedwith a cannulation. The insertion handle 1022 may include a third sensor1032.

The landmark identifier 1016 may include a second sensor 1020. Thelandmark identifier 1016 may guide a drill bit 1018, and the drill bit1018 may be connected to a drill (not shown). The second sensor 1020 maybe connected to the control unit 1012, either by wire or wirelessly. Thefield generator 1014 may be included in or on the landmark identifier1016, in which case, the second sensor 1020 may be omitted.

The probe 1029 may include a wire 1030, a tape 1034, and a stop 1036.The tape 1034 may be about 0.125 inch wide by about 0.060 inch thick 300series stainless steel fish tape available from Ideal Industries, Inc.of Sycamore, Ill. However, those of ordinary skill in the art wouldunderstand that other materials and other sizes may be used. Forexample, any narrow band of polymer, composite material, or metal may beused as the tape 1034, but it may be preferred to use a non-ferrousmetal. The tape 1034 may be coiled before placement into theintramedullary nail 1024. Coiling of the tape 1034 may cause it to havea natural curvature. The tape 1034 may have, in some implementations, arectangular geometry that assists in orienting the tape as it is placedinto a cannulation of the intramedullary nail 1024. An oval, square, orcircular geometry also may be used. The wire 1030 may be operativelyconnected to the tape 1034. For example, this may be accomplishedthrough the use of an adhesive or fastener. The tape 1034 may includegraduations or detents to indicate a depth of the tape as it is insertedinto the implant.

A first sensor 1026 is connected to the control unit 1012, either bywire or wirelessly. The first sensor 1026 is connected through the useof the wire 1030 and a connector 1038. The connector 1038 may beomitted. The first sensor 1026 may be connected to a distal end of thetape 1034, and the stop 1036 may be connected to a proximal end of thetape 1034.

The probe 1029 may include a sensor housing (not shown) to house thefirst sensor 1026. The sensor housing may be attached to the tape 1034.The sensor housing may be made of a non-ferrous material, such as apolymer, a composite, or a metal. The sensor housing may include anappropriate strain relief to shield the wire 1030 from stresses. Thesensor housing may be constructed and arranged to be large enough tohold the first sensor 1026 but small enough to fit through thecannulation of the insertion handle or the implant. Further, the sensorhousing may be constructed and arranged to be long enough to allowpassage through intramedullary nail bends, intramedullary nail bow,and/or bends in relevant instrumentation. Geometry of the leading andtrailing faces of the sensor housing may be designed such that thesensor housing does not catch or snag on the cannulation of theinstrumentation or implant.

The stop 1036 may be used to control the placement of the sensor 1026and probe 1029. If the tape 1034 is a fixed length and the distance isknown from the end of the insertion handle to the hole 1028, repeatableplacement of the first sensor 1026 may be achieved. The tape 1034 may beof sufficient length such that the sensor 1026 is aligned with the hole1028, adjacent the hole 1028, or offset from the hole 1028. As discussedbelow, the probe 1029 may be used to position the sensor with the hole1028 or other landmark.

The insertion handle 1022 may be omitted. In such a case, a differenttape length may be selected such that the stop 1036 engages a portion orend of the nail 1024.

FIG. 26 is a partial detailed view of the intramedullary nail 1024, thesensor 1026, and the hole 1028. The sensor 1026 may be aligned with thehole 1028, adjacent the hole 1028, or offset from the hole 1028. Thesensor 1026 is generally adjacent to the hole 1028.

In use, the intramedullary nail 1024 is placed into the bone 100. Theinsertion handle 1022 may be attached to the intramedullary nail 1024.The probe 1029 is fed through the cannulation of the insertion handle1022 and into the cannulation of the intramedullary nail 1024 until thestop 1036 engages the insertion handle 1022. In one particularimplementation, the wire 1030 is connected to the control unit 1012, andthe sensors 1026, 1020, and 1032 are calibrated using the control unit1012. The probe 1029 may be removed after calibration. If so, the thirdsensor 1032 and a transformation matrix may be used to identify therelative position of the second sensor 1020 and hence landmarkidentifier 1016. Optionally, the user may use transfixion elements, suchas screws, to first lock the proximal end of the intramedullary nail. Anoperator uses the landmark identifier 1016 and the first sensor 1026 toidentify the landmarks 1028. For example, in the case of intramedullarynail fixation, a surgeon uses the landmark identifier 1016 to identifythe blind transfixion holes and drill through the holes for placement ofa transfixion element.

FIG. 27 illustrates a packaging implementation. In general,intramedullary nails must be sterilized before implantation. If thesensor is installed in the intramedullary nail prior to serialization,the sensor may lose its calibration during the serialization process,particularly if the sterilization process involves radiation. Forexample, gamma radiation may be used to sterilize hermetically sealedcomponents, such as the sensor. The implementation depicted in FIG. 27illustrates a way to maintain the sterilization of the intramedullarynail while allowing for recalibration of the sensor. The package FIG. 27may include a first package 1040, a second package 1042, a firstconnector 1044, a second connector 1046, and a cable 1048. In thedepicted implementation, a sensor (not shown) and intramedullary nail1024 are located within the first package 1040. Alternatively, the probe1029 and the sensor are located within the first package 1040. In yetanother example, only the sensor is located within the first package1040. A memory device (not shown) may be connected to the sensor. Thememory device may be used to store a calibration transformation matrix(x1, y1, z1, x2, y2, z2) as well as other data, such as length and sizeof the intramedullary nail or the probe. The memory device may bemounted to or placed on the intramedullary nail 1024 or the probe 1029.The first connector 1044 is electrically connected, but removablyattached, to the second connector 1046. The first connector 1044 is alsoelectrically connected to the sensor or the memory device. The firstpackage 1040 maintains the sterilization of the device held within. Thecable 1048 is electrically connected to the second connector 1046 and astorage device (not shown). The calibration for the sensor is downloadedfrom the storage device and transmitted through the connectors 1044,1046 to the sensor or the memory device. The calibration step may beperformed during manufacturing of the system or immediately prior toimplantation of the implant.

FIG. 28 illustrates a method of connecting the system 1010 to a network.FIG. 28 illustrates a network 1060, a computing device 1050, the cable1048, the second connector 1046, the first connector 1044, and theintramedullary nail 1024. In the depicted implementation, a sensor (notshown) is located within the intramedullary nail 1024. Alternatively,the sensor may be attached to the probe 1029 or freestanding. Theintramedullary nail 1024 may be wrapped in packaging, such as the firstpackage 1040 and/or second package 1042 but this is not always the case.A memory device (not shown) may be connected to the sensor. The memorydevice may be used to store a calibration transformation matrix (x1, y1,z1, x2, y2, z2) as well as other data, such as length and size of theintramedullary nail or the probe. The memory device may be mounted to orplaced on the intramedullary nail 1024 or the probe 1029. The network1060 maybe a local area network or a wide area network. The computingdevice 1054 is connected to the network 1060. The network communicationmay be encrypted. The cable 1048 connects the computing device 1054 tothe sensor or the memory device through the use the connectors 1044,1046. In this way, the sensor calibration may be downloaded from thecomputing device 1054 and/or the network 1060. While the depictedimplementation illustrates the sensor within the intramedullary nail,this is not always the case. The sensor may be attached to the probe orfreestanding. The memory device may be located within the control unit,and the control unit is connected to the network to download thecalibration data.

FIG. 29 illustrates a system 1110 for identifying a landmark in a fourthimplementation. The system 1110 may include a control unit 1112, a fieldgenerator 1114, a landmark identifier 1116, an intramedullary nail 1124,a drop 1136, and a probe 1129. The control unit 1112 may be included aspart of the processor described above or may be a separate unit. Theintramedullary nail 1124 is inserted into the bone 100, and theintramedullary nail 1124 has a hole or landmark 1128. The fieldgenerator 1114 is connected to the control unit 1112, either by wire orwirelessly. In the depicted implementation, an insertion handle 1122 isremovably attached to the intramedullary nail 1124. The insertion handle1122 and/or the intramedullary nail 1124 may be formed with acannulation. The insertion handle 1122 may include a third sensor 1144.The drop 1136 may include a fourth sensor 1139.

The landmark identifier 1116 may include a second sensor 1120. Thelandmark identifier 1116 may guide a drill bit 1018, and the drill bit1018 may be connected to a drill (not shown). The second sensor 1120 maybe connected to the control unit 1112, either by wire or wirelessly. Thefield generator 1114 may be included in or on the landmark identifier1116, in which case, the second sensor 1120 may be omitted.

The probe 1129 may include a wire 1130, a tape 1134, and a stop 1136. Asshown below, the probe may be more unitary in structure as well. Thetape 1134 may have, in some implementations, a rectangular geometry thatassists in orienting the tape as it is placed into a cannulation of theintramedullary nail 1124. The wire 1130 may be operatively connected tothe tape 1134. For example, this may be accomplished through the use ofan adhesive or fastener. A first sensor 1126 is connected to the controlunit 1112, either by wire or wirelessly. The first sensor 1126 isconnected through the use of the wire 1130. In some implementations, adetachable connector may be used. The first sensor 1126 may be connectedto a distal end of the tape 1134, and the stop 1136 may be connected toa proximal end of the tape 1134. The stop 1136 may be used to controlthe placement of the sensor 1126. If the tape 1134 is a fixed length andthe distance is known from the end of the insertion handle to thelandmark 1128, repeatable placement of the first sensor 1126 may beachieved. The tape 1134 may be of sufficient length such that the sensor1126 is aligned with the landmark 1128, adjacent the landmark 1128, oroffset from the landmark 1128.

In use, the intramedullary nail 1124 is placed into the bone 100. Theinsertion handle 1122 may be attached to the intramedullary nail 1124.The probe 1129 is fed through the insertion handle 1122 and into theintramedullary nail 1124 until the stop 1136 engages the insertionhandle 1122. In one particular implementation, the wire 1130 isconnected to the control unit 1112, and the sensors 1126, 1120, and 1132are calibrated using the control unit 1112. The probe 1129 may beremoved after calibration. If so, the third sensor 1132 and/or thefourth sensor 1139 and a transformation matrix may be used to identifythe relative position of the second sensor 1120 and hence targeter 1116.Optionally, the user may use transfixion elements, such as screws, tofirst lock the proximal end of the intramedullary nail. An operator usesthe landmark identifier 1116 and the first sensor 1126 to identify thelandmarks 1128. For example, in the case of intramedullary nailfixation, a surgeon uses the landmark identifier 1116 to identify theblind transfixion holes and drill through the holes for placement of atransfixion element.

FIG. 30 illustrates a first method for using the system to identify alandmark. The method begins at step 1210. In step 1212, the sensor isplaced in the nail. In step 1214, the insertion handle is connected tothe nail, and the drop is attached to the insertion handle. In step1216, the control unit is connected to the sensor. In step 1218, thesensor is calibrated. In step 1220, the sensor is aligned with the hole.In step 1222 the sensor position is recorded through the use of thecontrol unit. In step 1224, the sensor is removed from the nail. In step1226, the nail is implanted into the bone. In step 1228, the hole isdrilled using the targeter. The method stops in step 1230.

FIG. 31 illustrates a second method for using the system to identify alandmark. In step 1310, the tracking system is turned on. In step 1312,the intramedullary nail is inserted into bone. In step 1314, the probe1129 is inserted into the intramedullary nail canal at a predeterminedlocation and orientation using the stop 1136 and detents spaced along alength of the probe 1129. In step 1316, there is a decision whether theintramedullary nail needs to be locked proximally before distally. Ifyes, then in step 1326 the drop is attached to the nail. In step 1328,an offset is calculated between the probe and the drop. In other words,a transformation matrix is created. Alternatively, the drop is notconnected to the intramedullary but instead a sensor mounted in theinsertion handle is used to calculate an offset. In step 1330, the probeis removed from the nail. In step 1334, the nail is locked proximally.This may be accomplished through the use of the landmark identifier, amechanical jig, or by manual operation. In step 1336, the landmarkidentifier is used to target the drill. In step 1338, the hole isdrilled for the distal screw. In step 1340, the intramedullary nail islocked distally. On the other hand, if the decision is to lock distallyfirst, then in step 1318 the landmark identifier and probe are used totarget the drill bit. In step 1320, the hole is drilled for the distalscrew. In step 1322, the intramedullary nail is locked distally. In step1324, the probe is removed from the intramedullary nail. In step 1324,the intramedullary nail is locked proximally. This may be accomplishedthrough the use of the landmark identifier, a mechanical jig, or bymanual operation.

FIG. 32 illustrates a system for measuring depth of drill bit placement.The system 1400 may include a stator 1410 and a slider 1412. The stator1410 and the slider 1412 form a capacitive array that can sense relativemotion. Moving the stator 1410 and the slider 1412 in a linear relationrelative to one another causes a voltage fluctuation that can beinterpreted and used to determine the distance traveled. In someimplementations, an electronic measuring circuit (not shown) and theslider 1412 may be housed inside the landmark identifier, and the drillbit may be specially constructed to have the stator 1410 along outersurface so that the stator 1410 and the slider 1412 are in very closelinear proximity to each other. The linear movement of the drill bitstator 1410 induces a voltage in the receiving slider 1412 which isinterpreted by the electronic measuring circuit as a distancemeasurement. The distance measurement may be sent to the control unitand/or displayed on the monitor. Capacitive sensors are highlysusceptible to moisture, and so some implementations may be made toprevent liquids, such as bodily fluids, from traveling between thestator 1410 and the slider 1412. O-rings or some other similar form ofwipes can be incorporated within the landmark identifier in order tokeep the drill bit substantially moisture free.

Alternatively, the drill bit can be provided with reference markings,such as distance measurements, and a jig can be used to determine thedepth of insertion into bone of the drill bit. For example, a separatesleeve (not shown) or a drill sleeve of a landmark identifier, such asthe tube 24 discussed above, can be placed over the drill bit beforedrilling such that a first end of the sleeve, such as the tip 22, isplaced against the bone surface to be drilled. When the drill bit ispassed through the sleeve and into the bone, a second end of the sleeveserves as a reference portion to indicate the depth of insertion of thedrill bit. For example, a marking on the drill bit that is aligned withthe reference portion denotes a depth of insertion of the drill.Similarly, depth of insertion of a fastener, such as a locking screw,can be gauged in a similar manner. For example, a driver sleeve can beprovided over a fastener and a fastener driver. The fastener driver caninclude a laser etched image of all or a portion of the fastener, suchas the fastener head, on an exterior surface and/or can include one ormore other reference marks, such as circumferential grooves or othermarkings. In use, as the fastener is inserted into a bone, the image ofthe fastener and/or the other reference marks move relative to areference portion of the sleeve, such as the end of the sleeve. Based onthe relative positions of the reference portion of the sleeve and theimage or other markings, the depth of the insertion of the fastener canbe determined. For example, when the end of the sleeve is aligned with acircumferential groove of the driver that is positioned immediatelybelow an image of the head of the fastener, the sleeve indicates thatthe base of the head of the fastener is flush with the bone. So long asthe sleeve is not covering any part of the image of the head, thisindicates that the actual head of the fastener is entirely above thesurface of the bone.

FIGS. 33A and 33B illustrate another system for measuring depth of drillbit placement. The system 1500 may include a reflective code wheel orstrip 1510, a lens 1512, and an encoder 1514. The lens 1512 focuseslight onto bar of the code strip 1510. As the code strip 1510 rotates,an alternating pattern of light and shadow cast by the window and bar,respectively, falls upon photodiodes of the encoder 1514. The encoder1514 converts this pattern into digital outputs representing the codestrip linear motion. The encoder is an Avago Technologies AEDR-8300Reflective Optical Encoder available from Avago Technologies of 350 WTrimble Road, San Jose, Calif. Alternatively, the Avago TechnologiesADNS-5000 One Chip USB LED-based Navigation System may be used. Theencoder and its supporting electronics may be mounted inside thelandmark identifier so that its input region is oriented toward a“window” in the landmark identifier cannulation. Markings, such as darkcolored concentric rings or bright reflective rings, may be added to thedrill bit in order to enhance the visibility of the bit to the encoder.These markings could also be used to denote the starting zero point formeasurement. As the drill bit moves linearly within the landmarkidentifier, the encoder measures the movement of the drill bit. Thedistance measurement may be sent to the control unit and/or displayed onthe monitor.

FIG. 34 illustrates yet another system for drill depth measurement. Thesystem 1600 utilizes a Linear Variable Differential Transformer (LVDT)1612. An LVDT is a type of electrical transformer used to measure lineardisplacement. The LVDT 1612 may include a plurality of solenoid coils1618 placed end-to-end around a tube 1610, which is the landmarkidentifier in the depicted implementation. In FIG. 34, the center coilis the primary coil and the outer two coils are the secondary coils. Acylindrical ferromagnetic core 1610, such as the drill bit, slides alongthe axis of the tube. An alternating current 1614 is driven through theprimary coil, causing a voltage to be induced in each secondaryproportional to its mutual inductance with the primary. A pickup sensor1616 measures the magnitude of the output voltage, which is proportionalto the distance moved by the core (up to its limit of travel). The phaseof the voltage indicates the direction of the displacement. Because thesliding core does not touch the inside of the tube, it can move withoutfriction, making the LVDT a highly reliable device. The absence of anysliding or rotating contacts allows the LVDT to be completely sealedagainst the environment. The distance measurement may be sent to thecontrol unit and/or displayed on the monitor.

FIGS. 35-37 illustrate an insertion handle 1700 (FIG. 35) and anadjustable stop 1800 (FIGS. 37-38). The insertion handle 1700 a stem1710 that connects to an implant, such as an intramedullary nail (notshown), at an end portion 1712. The insertion handle 1700 may include aquick connect 1716 for attachment to a drop, proximal targeting device,or some other instrument or apparatus. The insertion handle may includea top portion 1714, which may include a hole and/or an alignmentfeature. The adjustable stop 1800 may include a slot 1810, an alignmentmember 1812, and a fastener hole 1814.

In FIGS. 35-37, the adjustable stop 1800 may be removably attached tothe top portion 1714 of the handle 1700. The adjustable stop may beintegrally formed with the insertion handle 1700. In yet otherimplementations, the adjustable stop may be permanently attached to theinsertion handle 1700. The alignment member 1812 fits within analignment feature of the top portion to prevent rotation of theadjustable stop. A fastener (not shown) may be placed through thefastener hole 1814 to attach the adjustable stop to the insertion handle1700. The tape 1034, 1134 may be placed through the slot 1810, throughthe stem 1710, and into the intramedullary nail cannulation. The slot1810 may have a shape to match the geometry of the tape and/or probe1129 to aid in its insertion or to prevent rotation of the tape. Thetape 1034, 1134 or probe 1129 may include markings, graduations, ordetents to indicate an appropriate depth for the given nail length. Theadjustable stop 1800 may include a locking mechanism (not shown) totemporarily lock the tape 1034, 1134 at a particular depth. In itssimplest form, the locking mechanism may be a fastener that frictionallyengages the tape 1034, 1134.

FIG. 38 illustrates a method for calibrating the system for identifyinga landmark. Calibration is necessary for accuracy. The method begins atstep 1900, which may include powering up the system. In step 1910, theprobe and the landmark identifier are removed from packaging, if any,and scanned. The drop is also scanned. Scanning may include reading abar code using a bar code reader. Scanning causes the system to retrieveoffset sensor values that correspond to the bar code from a look uptable in step 1912. The look up table may be local or accessed over anetwork, such as the Internet. Alternatively, the probe and the landmarkidentifier may include a serial number or other unique identifier, andthe unique identifier is used in conjunction with the look up table toretrieve offset sensor values. The offset sensor values are stored inlocal memory of the system in step 1914. In step 1916, the user placesthe probe relative to the implant and attempts to track a landmark usingthe landmark identifier in step 1916. In step 1918, there is a decisionwhether the calibration is correct. If so, the method ends in step 1920.Otherwise, new offset values are retrieved in step 1912.

FIG. 39 illustrates an implementation combining a landmark identifier, afield generator and a drill sleeve. The handheld landmark identifier2016 houses an electromagnetic field generator (not shown) which mayinclude one or more induction coils or other elements to create asuitable electromagnetic field or fields. The electromagnetic fieldgenerator is mounted in or on an autoclavable material and encapsulatedin an autoclavable housing body 2018 that may be easily sterilized, andwhich is removably engageable with a tool. The relative orientation andposition of the induction coils or elements in the landmark identifier2016 may be selected to optimize the balance between the qualities andstrength of the electromagnetic field or fields and their interactionwith the sensor and the weight, size, form factor and ergonomics of theidentifier 2016. At least three induction coils (not shown) may bemounted in or on the autoclavable material.

For example, as shown in FIG. 39a , the landmark identifier 2016includes a mounting structure 2030. The mounting structure 2030 includeselements 2031, such as receptacles or posts, that are configured toreceive induction coils of the electromagnetic field generator atlocations and orientations. For example, each the elements 2031 isformed in or on the mounting structure 2030 such that each element 2031has a size and a shape that conforms to a portion of an induction coilsuch that the element allows an induction coil to be disposed within oron the element 2031 at predetermined locations and at predeterminedorientations. The induction coils can then be secured within or on theelements using adhesive, mechanical fasteners, or other securing devicesor techniques. Lead wires for the coils can be routed within channels2033 formed in the mounting structure 2030. Alternatively, the elementscan be formed having other shapes, such as a post, and the position andorientation of each induction coil can be controlled during assembly bya jig or other assembly technique. Placing the induction coils in thepredetermined locations and orientations allows use of predeterminedcalibration parameters for the field generator and/or for sensors. As afurther alternative, the elements 2031 can be formed on the mountingstructure 2030 in random locations and orientations, but following asubsequent sterilization process, the locations and orientations of theelements 2031 will remain substantially the same as further discussedbelow. If random locations and orientations are used, the fieldgenerator and/or the sensors may be calibrated to account forcharacteristics of an electromagnetic field generated by the coils.

The autoclavable materials of the landmark identifier 2016 allow thelandmark identifier 2016 to be sterilized or autoclaved multiple timeswithout degradation of the autoclavable materials, internal components,or operational performance of the landmark identifier. For example, themounting structure 2030 on which the coils and/or other electromagneticfield generating components are mounted is formed of a material thatdoes not adversely interfere with a generated electromagnetic field andwhich can be subjected to sterilization processes, includingautoclaving. For example, the internal body can be formed from aglass-reinforced epoxy laminate, such as a NEMA grade G-11 glassreinforced epoxy laminate (VETRONITE G11) or equivalent. Alternatively,the mounting structure 2030 can be formed from another material that isdimensionally-stable at temperatures, pressures, humidity levels, andother environmental conditions associated with autoclaving and/or othersterilization processes. Particularly, the mounting structure 2030 isformed from a material that does not substantially expand, contract,warp, soften, or undergo any other substantial structural change duringan autoclave process, referred to as a dimension stable autoclavablematerial. Thus, the positions and orientations of the coils and/or othercomponents mounted on the mounting structure 2030 are not substantiallyaltered during the autoclave process. For example, the orientation ofone or more of the coils does not change by more than 2 degrees in anydirection, and the locations of the coils does not change by more than0.005 inches in any direction during an autoclave process. In additionto the glass-reinforced epoxy laminate mentioned above, suitablematerials including those of carbon-fiber reinforced materials for themounting structure 2030 include ORTHTEK RP, ORTHTEK WF, TECACOMP CF60,TECAPEEK CF30-XP98, ULTEM 1000, ULTEM 2300, Zacton 350, Garolite G-7,Garolite G-11, Garolite G-10/FR4, Garolite G9. In certainimplementations, the material for the mounting structure 2030 has aflexural strength of at least about 10,000 psi. Additional materialsinclude non-magnetic metals such as cobalt chrome, titanium, or 300series stainless steel.

Optionally, the mounting structure 2030 can include hollow portions orlightweight inserts in areas 2037 that do not interfere with the desiredlocations of the elements 2031 in order to reduce the weight of thelandmark identifier 2016 to about five pounds, or less, for example,and/or to achieve a desired balance of weight distribution around thelandmark identifier 2016. For example, the landmark identifier 2016 canhave a center of gravity located generally within the opening, such asopening 2035 (FIG. 39a ), to achieve rotational or radial balance and/orprevent rotational bias of the landmark identifier 2016 about theopening, such as rotation induced by gravity if the center of gravity islocated outside the opening of the landmark identifier. For example,openings can be formed in one or more of the areas 2037, or in otherareas that do not adversely affect the placement of the components ofthe field generator and/or the structural characteristics of themounting structure, and hollow inserts can be installed in the openings.Similarly, lightweight foam material can be included in the areas 2037.The size and location of the openings, and the difference in density ofthe material inserted in the openings compared to the density of thematerial of the mounting structure 2030 can be selected to control thelocation of the center of gravity of the landmark identifier 2016.

The mounting structure 2030 is surrounded by a first covering 2018 aformed from a first material, such as an overmolding of VMQ siliconematerial #71385C available from Minnesota Rubber & Plastics, 1100 XeniumLane N., Minneapolis, Minn. 55441. The first covering 2018 a shields themounting structure and the components of the field generator from damagefrom impact during use, as well as from moisture during the autoclaveprocess. Thus, the first material forming the first covering 2018 a isthermally-stable at temperatures up to the autoclave temperature, forexample, 120 degrees Celsius. Additionally, the first material hassuitable properties for water absorption, electrical conductivity, andthermal conductivity, such that the components of the electromagneticfield generator are not damaged by heat or moisture, and such that theoperation of the components is not affected by contact with the firstmaterial. Suitable materials for the first covering 2018 a includetitanium, ceramic, polypropylene (PP), polypropylene copolymer (PPCO),polycarbonate (PC), polymethylpentene (PMP), polytetrafluoroethylene(PTFE) resin, polymethyl methacrylate (PMMA or acrylic), ethylenetetrafluoroethylene (ETFE), ethylene chlorotrifluoroethlyene (ECTFE),fluoro ethylene propylene (FEP), polyether imide (PEI), perfluoroalkoxy(PFA), polyketone (PK), polyphenylene oxide (PPO), polysulfone (PSF),polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), silicone, andthermoplastic elastomers (TPE), or combinations of these materials.

Optionally, the mounting structure 2030 can be covered with acompressible closed-cell foam material before applying the firstcovering 2018 a. For example, the compressible closed-cell foam materialcan be injection molded over the mounting structure 2030 such that thefoam material fills any openings formed in the areas 2037. Thecompressible foam material allows a user to comfortably grasp thelandmark identifier 2016 and lowers the density of the landmarkidentifier compared to an implementation where silicone of the firstcovering 2018 a is molded directly over the mounting structure 2030. Thesilicone or other material, as discussed above, of the first covering2018 a can then be molded, or otherwise formed, over the foam. Theclosed-cell structure of the foam can limit the penetration of thesilicone or other material of the first covering 2018 a into the foam topreserve the weight-reducing feature provided by the foam. In someimplementations, grooves, channels, pockets or other features can bedefined in the foam, and the first covering 2018 a can fill space of thefeatures to increase the bond strength between the first covering andthe foam, and to increase the strength of the landmark identifier 2016.

Optionally, the housing 2018 also includes a second covering 2018 b thatmay provide an additional layer of protection or insulation, oraesthetic at an outer edge of the housing 2018. The second covering 2018b may be formed from a second material, such as an overmolding of VMQsilicone material #71325C available from Minnesota Rubber & Plastics,1100 Xenium Lane N., Minneapolis, Minn. 55441. Alternatively, the secondcovering 2018 b can be formed of the materials discussed above withrespect to the first covering 2018 a. Optionally, the second covering2018 b and/or exposed parts of the first covering 2018 a can includeexternal surface texture formed over at least selected portions of thefirst covering 2018 a and/or the second covering 2018 b that areintended to be gripped by a user holding the landmark identifier 2016.For example, a rough surface texture, ribs, dimples, bumps or othersurface texture can be provided on the exterior of the second covering2018 b. If desired, the external surface texture of the second covering2018 b can be formed only in locations where the landmark identifier2016 is intended to be gripped by a user. Thus, the external surfacetexture can indicate to a user where the landmark identifier 2016 shouldbe gripped during use.

The housing 2018 also includes a coupling member 2018 c that passesthrough the internal body and that engages one or more attachablecomponents. A drill sleeve attachment 2020, as illustrated in FIG. 39b ,is coupled to the coupling member. Particularly, the drill sleeveattachment 2020 includes a shaft 2041 that is received in an opening2035 (FIG. 39a ) of the mounting structure 2030. The drill sleeveattachment also includes a frustoconical portion 2043 and a threadedportion 2045 that engage corresponding structures of the coupling member2018 c, such as a frustoconical seat and an internal thread.Alternatively, the portion 2043 and corresponding seat can be formedwith other matching geometries (e.g., cylindrical or conical) thatassist in limiting play between, and securing, the location andorientation of the drill sleeve attachment 2020 relative to the couplingmember 2018 c. Like the components of the electromagnetic fieldgenerator described above, the location and orientation of the couplingmember 2018 c and the drill sleeve attachment 2020 and the drill sleeve2022 impact the accuracy of the landmark identifier 2016 in use.Therefore, the coupling member 2018 c and the drill sleeve attachment2020 and the drill sleeve 2022 are formed from dimension stableautoclavable materials as described, such as polysulfone, ornon-magnetic metals such as cobalt chrome, titanium, or 300 seriesstainless steel. For example, the coupling member 2018 c and the drillsleeve attachment 2020 can be formed from GEHR PPSU polyphenylsulfoneRAL 9005 Black (Solvay Radel R-5500) or equivalent. Alternatively, thecoupling member 2018 c and the drill sleeve attachment 2020 can beformed of the dimension stable autoclavable materials discussed abovewith respect to the mounting structure 2030. Also the coupling member2018 c and the drill sleeve attachment 2020 and the drill sleeve 2022can be an integral part of the landmark identifier 2016.

The particular landmark identifier 2016 illustrated in FIG. 39 may alsoinclude the removable drill sleeve attachment 2020 and the drill sleeve2022 with a serrated tip 2024, though different components andconstructions can be included as mentioned elsewhere. The sleeveattachment 2020 and drill sleeve 2022 can be formed as a single unit oras separate units connected to each other by adhesives or otherconnection means known to one skilled in the art. For illustrationpurposes, the sleeve 2022 as illustrated in FIG. 39 is a drill sleeve,but it can also be a larger size sleeve such as a screw driver sleeve orother sleeves as selected by the surgeon, or other components asdisclosed herein. For example, various drill sleeves 2022 havingdifferent sizes may be used to accommodate different-sized drill bits,and drill sleeves 2022 having different lengths may be used toaccommodate, for example, varying patient tissue thickness. To changesleeves or other components, the surgeon unscrews the sleeve attachmentand replaces it with another sleeve attachment of choice and itscorresponding sleeve. As discussed above, the drill sleeve 2022 and/orthe screw driver sleeve can be used to gauge the depth of insertion of adrill bit or a fastener using reference markings formed in the drill bitor on the screw driver and a reference portion of the landmarkidentifier. For example, when the drill sleeve 2022 is disposed againsta bone, the opening of the landmark identifier through which the drillbit is inserted can serve as the reference portion.

Unlike the landmark identifier 18 illustrated in FIG. 9, the landmarkidentifier 2016 depicted in FIGS. 39-40 does not require the secondsensor 20 illustrated in FIG. 9 because the origin of the global space(the area in which the electromagnetic field is generated) can bedefined within the landmark identifier 2016. One axis of the globalspace co-ordinate system can be the longitudinal axis of the drillsleeve or other component 2022. In that situation, the other two axes ofthe global space co-ordinate system can be defined by planes orthogonalto that longitudinal axis and to each other. Advantages of incorporatingthe field generator into the landmark identifier 2016 include a smallersize field generator because it can be brought into the local workingspace (area which may include the landmarks such as implant holes thatare to be targeted for screw placement) therefore requiring a smallerelectromagnetic field. The global space and local working space becomethe same or at least correspond more closely spatially when the landmarkidentifier 2016 with its field generator brought into the vicinity ofthe landmark, implant or probe sensor (not shown). Because theelectromagnetic field size requirement is smaller, the induction coilswithin the field generator can be smaller which therefore reduces thesize and weight of the handheld field generator to make it moremanageable for handheld usage. In addition, use of the landmarkidentifier 2016 eliminates the necessity of X-ray devices for targetingof transfixion elements, such as radiation-emitting, fluoroscopic“c-arms,” which have traditionally been used during tibial and femoralnail cases to achieve proper distal screw placement. A recent studyquantified the impact the landmark identifier 2016 has on both radiationlevels and case length. Use of the landmark identifier 2016 to achieveproper distal screw placement was shown to eliminate 36 seconds offluoroscopy exposure (0.785 radiation absorbed doses, or rads) duringtibial fracture cases and 49 seconds during femoral fracture cases(2.362 rads). In addition, the accuracy and the consistency in thedegree of precision in targeting and locking of the distal screwsoffered by use of the landmark identifier 2016 reduced distal lockingtime by at least 50% when compared to, for example, c-arm techniques fortargeting and locking the distal screws.

A light may be provided in an area of the landmark identifier/fieldgenerator/drill 2016, such as the area 2025 to indicate to the user thatpower is being supplied to the landmark identifier/field generator/drill2016. In FIG. 41, the drill sleeve 2022 has been removed and thelandmark identifier 2016 has been engaged with a screw driver 2100 forfixing the implant to the bone. As shown in FIG. 41, the housing 2018 ofthe landmark identifier 2016 may include one or more indentations 2018 dfor finger placement to allow the user to comfortably place his or herhand around the landmark identifier 2016. In the implementation depictedin FIG. 41, there are six indentations. Additionally, the texture anddimension of an exterior surface of the housing 2018 can be configuredallow a user to comfortably and securely grip the housing 2018.Additionally, or alternatively, the landmark identifier 2016 can beattachable to a tool, such as being attachable to a housing of the screwdriver 2100.

The material selection for the landmark identifier 2016 of FIG. 39 whichhouses the field generator can be optimized for weight and stabilityafter multiple autoclave cycles. Any autoclavable material can be used,and the materials are preferably non-magnetic or weak magnetic to avoidor minimize interference with the electromagnetic fields. Exemplarymaterials include ceramic, autoclavable polymers such as polypropylene(PP), polypropylene copolymer (PPCO), polycarbonate (PC),polymethylpentene (PMP), polytetrafluoroethylene (PTFE) resin,polymethyl methacrylate (PMMA or acrylic), ethylene tetrafluoroethylene(ETFE), ethylene chlorotrifluoroethlyene (ECTFE), fluoro ethylenepropylene (FEP), polyether imide (PEI), perfluoroalkoxy (PFA),polyketone (PK), polyphenylene oxide (PPO), polysulfone (PSF), polyvinylchloride (PVC), polyvinylidene fluoride (PVDF), silicone, orthermoplastic elastomers (TPE), and still other autoclavable materialswhich will be apparent to those skilled in the art, includingcombinations of the above.

FIG. 42 illustrates another insertion handle 2122, an adjustable stop1801, a probe 2129 and a sensor 2126 located within or on a body 2129 aof the probe 2129. The insertion handle 2122 is removably attached to anorthopaedic implant, such as an intramedullary nail. The probe 2129includes a cable 2130 and a connector 2131 for connection to a processorfor use in targeting landmarks of the intramedullary nail, or otherimplant. The probe 2129 also includes a grip 2132 that secures the cable2130 to the body 2129 a to prevent tension forces applied to the cable2130 from damaging the sensor 2126 and/or the electrical connectionbetween the sensor 2126 and the cable 2130. The adjustable stop 1801 andan alternative stop 1803 are also illustrated in FIGS. 43 and 44. Thestop 1801 and the stop 1803 each include a push button actuator 1802.The stop 1801 includes a thumb wheel 1806 that is used to turn athreaded bolt 1807 for attaching the stop 1801 to an insertion handlewhile the stop 1803 includes a knob clamp 1804 that is also connected toa threaded bolt 2531 (FIG. 58). The probe 2129 may be equipped withdetents or markings to assist the user in placing the probe 2129 andsensor 2126 in the correct position.

The system may include different stops, such as stops 1801, 1803,depending upon the particular surgical approach contemplated. Forexample, the surgical approach in the case of retrograde placement of anintramedullary nail may utilize the stop 1801, whereas antegrade placeplacement of an intramedullary nail may favor use of the stop 1803.Other surgical approaches may yet require other variations.

Now referring to FIG. 45, the adjustable stop 1803, an insertion handle2123, and the probe 2129 are illustrated in an assembled configurationattached to an intramedullary nail 2125. A distal portion 2124 of theinsertion handle 2123 is attached to a proximal head 2126 of theintramedullary nail 2125. The insertion handle 2123 is connected to theintramedullary nail 2125 through the use of a cannulated bolt (notshown). Alternatively, the insertion handle 2123 can be connected to theintramedullary nail 2125 using a quick-connect mechanism, or otherattachment device.

The adjustable stop 1803 is attached to a proximal surface 2127 of theinsertion handle 2123. The adjustable stop 1803 has a complimentarymating portion such that when the stop 1803 is connected to theinsertion handle 2123, the stop 1803 is located or fixed relative to theinsertion handle 2123 within three degrees of freedom. The probe 2129 isinserted through a hole 1805 of the adjustable stop 1803, through thedistal portion 2124 of the insertion handle 2123, through the cannulatedbolt, and into a cannulation (not shown) of the intramedullary nail2125. The probe 2129 includes the sensor 2126 (FIG. 42) locatedproximate a distal end (not shown). The sensor 2126 (FIG. 42) iselectrically connected to the cable 2130 that includes the connector2131 for transmitting signals from the sensor 2126 (FIG. 42) to acontrol unit (not shown).

FIG. 46 shows the adjustable stop 1801, the insertion handle 2122, andthe probe 2129 in an assembled configuration attached to anintramedullary nail 2155. The adjustable stop 1801 is mounted to aproximal surface 2147 of the insertion handle 2122 by rotating the thumbwheel 1806 to thread the bolt 1807 (FIG. 43) into a threaded connection(not shown) formed in the insertion handle 2122. The adjustable stop1801 has a complimentary mating portion such that when the stop 1801 isconnected to the insertion handle 2122, the stop 1801 is located orfixed relative to the insertion handle 2122 within three degrees offreedom. A distal portion 2144 of the insertion handle 2122 is attachedto a head 2156 of the intramedullary nail 2155. For example, theinsertion handle 2122 is connected to the intramedullary nail 2125through the use of a cannulated bolt (not shown). The probe 2129 isinserted through a hole 1808 of the adjustable stop 1801, through thedistal portion 2144 of the insertion handle 2122, through the cannulatedbolt, and into the head 2156 of the intramedullary nail 2155.

Now referring to FIG. 47, a proximal targeting probe 2161 and a distaltargeting probe 2171 are illustrated. The proximal targeting probe 2161includes a tape body 2163 and a sensor 2165 disposed within or on thetape body 2163 at a predetermined distance D1 from a reference point R1of the body 2163. The proximal targeting probe 2161 also includes acolor-coded grip 2167 that indicates that the probe 2161 is to be usedfor targeting proximal landmarks of an orthopaedic implant, such as theintramedullary nail 2155 of FIG. 46 and a cable 2169 for carrying asignal from the sensor 2165 to a control unit (not shown). The distaltargeting probe 2171 includes a tape body 2173 that is longer than thebody 2163 of the proximal targeting probe 2161. A sensor 2175 isincluded within or on the tape body 2173 at a second predetermineddistance D2 from a reference point R2 of the body 2173. The distaltargeting probe 2171 also includes a color-coded grip 2177 that is adifferent color than the grip 2167 and that indicates that the probe2171 is to be used for targeting distal landmarks of an orthopaedicimplant, such as the intramedullary nail 2155 of FIG. 46. A cable 2179is included to transmit a signal from the sensor 2175 to a control unit(not shown). The tape body 2163 of the proximal targeting probe 2161and/or the tape body 2173 of the distal targeting probe 2171 may have,in some implementations, a rectangular geometry that assists inorienting the tape body as it is placed into a cannulation of theintramedullary nail. An oval, square, or circular geometry also may beused. In some implementations, the tape body 2163 and the tape body 2173may be a hollow metal tube. Instead of color-coded grips, in someimplementations, each of the sensors 2165 and 2175 is connected to aProgrammable Read-Only Memory (PROM) microchip that stores thecalibration offset values and also stores an identifier that identifieswhether the probe is used for proximal or distal targeting. In that way,when the sensors 2165 and 2175 are both connected to a processor, suchas the processor 2327 of FIG. 51, the processor automatically identifiesthe type of targeting contemplated and may display such information on adisplay device, such as the display 2326.

The tape body 2163 and the tape body 2173 may include one or more bendsto bias at least a portion of the tape body 2163 and the tape body 2173against the wall of the cannulation of the orthopaedic implant. Biasinga portion of the tape body against the wall of the cannulation increasesthe repeatability of locating the sensors 2165 and 2175 relative tolandmarks. Alternatively, the probes 2161 and/or 2171 could be formedhaving dimensions approximately equal to dimensions of the cannulationof the intramedullary nail or other implant with which they are intendedto be used so that the proper location of the sensor within thecannulation can be repeatably achieved.

With reference to FIG. 48 and as an alternative to the pair of probesillustrated in FIG. 47, a targeting probe 2181 can be used to targetboth distal and proximal landmarks of an orthopaedic implant. The probe2181 is tubular and made from a non-magnetic metal, such as stainlesssteel. The probe 2181 includes a tape body 2183, a first sensor 2185disposed within a distal portion of the tape body 2183 and a secondsensor 2186 disposed within a proximal portion of the tape body 2183.The first sensor 2185 is located at a distance D3 from a reference pointR3 of the body 2183, which may be formed as a notch or detent, and thesecond sensor is located at a second distance D4 from the referencepoint R3.

In use, the first sensor 2185 is used to target a distal landmark of anorthopaedic implant, such as a distal locking aperture of anintramedullary nail, and the second sensor 2186 is used to target aproximal landmark of the orthopaedic implant, such as a proximal lockingaperture of the orthopaedic nail. In some implementations, theconstruction of the probe 2181 can be similar to the distal targetingprobe 2171 (FIG. 47), with the addition of the second sensor 2186. Theprobe 2181 also includes a grip 2187, which can be color-coded to bedistinguishable from the distal targeting probe 2171, and to indicatethat the probe 2181 can be used to target both distal and proximallandmarks of an implant. As discussed above, each of the sensors 2185and 2186 can be connected to a PROM or other storage device that storesreference values for use in determining a position of a landmarkidentifier, such as the landmark identifier 2016, relative to a landmarkof an implant. The PROMs also store identifiers that allow a processorto determine whether a received signal was generated by the distalsensor 2185 or the proximal sensor 2186.

Another alternative probe 2191 is illustrated in FIG. 49. The probe 2191includes a housing 2192 and a retractable/extensible body 2193 that canbe coiled within the housing 2192. A sensor 2195 disposed within thebody 2193 can be positioned at a first position P1 for targeting aproximal landmark of an implant, and can be positioned at a secondposition P2 for targeting a distal landmark of an implant. In someimplementations, the body 2193 can be formed as a concave metal stripthat tends to maintain a generally straight shape when extended from thehousing, but can also be coiled within the housing 2192. For example,the body 2193 may consist of layered, flexible stainless steel bi-stablespring bands that, when straightened, create tension within the springymetal bands to maintain a generally straight orientation, but coilwithin the housing 2192 when the tension is relieved. However, othertypes of materials can be used to form the body, including resilientplastic or rubber tubing or sheeting. Another alternative is to form thebody 2192 from nested segments of tubing that can extend and retract bysliding within adjacent tube segments. The probe 2191 can include arotary encoder, an optical device, or other measuring device or methodto determine a length of the body 2193 that is currently extending fromthe housing 2192. The determined length can be used to determine whetherthe sensor 2195 is positioned at a desired position, such as the firstposition P1 or the second position P2.

Now referring to FIG. 50, the adjustable stop 1801 is mounted to analternative insertion handle 2210. The insertion handle 2210 includes abody 2211 that is engaged with the head 2156 of the intramedullary nail2155 (also shown in FIG. 46). As an example, a cannulated bolt (notshown) may be used to connect the insertion handle 2210 to the head2156. The insertion handle 2210 includes a sensor 2213 for use intargeting a proximal landmark of the nail 2155, such as a proximallocking aperture 2157. The sensor 2213 is located within or on the body2211 at a predetermined distance D5 from the proximal locking aperture2157 when the insertion handle is attached to the nail 2155. The sensorcan be passive, or electrically powered by an internal battery (notshown) or an external power supply (not shown). The sensor 2213 may bemounted in a compartment that is unitary or integral with the body 2211,such as the exterior compartment 2216. Alternatively, the sensor 2213can be located in an internal compartment 2213 a, shown in FIG. 51. Theinsertion handle 2210 is made of plastic, but other materials couldalternatively be used.

The adjustable stop 1801 is used with a probe, such as the probe 2129(FIG. 46), for targeting distal landmarks of the nail 2155, such as adistal aperture 2159 (FIG. 51). As described above, the adjustable stop1801 can be attached to the insertion handle 2210 by a bolt 1807 (FIG.43) that engages a threaded bore 2215 that is aligned with alongitudinal through hole of the insertion handle 2210 (not shown) thatallows the probe to pass through the insertion handle 2210 and into thecannulation 2155 a (FIG. 51) of the nail 2155. The adjustable stop 1801also includes an arm 1809 that engages the body 2211 to prevent rotationbetween the adjustable stop 1801 and the insertion handle 2210.

Although not illustrated, the adjustable stop 1803 (shown in FIG. 45)can also be used with an insertion handle that includes an embeddedsensor for targeting proximal landmarks of an implant.

In use, an orthopaedic implant, such as the intramedullary nail 2155, isimplanted into bone. The insertion handle 2210 may be connected to theorthopaedic implant before or after implantation. Thereafter, a landmarkidentifier can be used for targeting of the proximal landmarks of theorthopaedic implant.

In some implementations, the distal landmarks are targeted prior to theproximal landmarks. As before, the insertion handle 2210 may beconnected to the orthopaedic implant before or after implantation. Thestop 1801 or the stop 1803 is connected to the insertion handle 2210. Aprobe is inserted into the stop, through the insertion handle 2210, andinto the orthopaedic implant, such as the nail 2155. The distallandmarks are targeted, transfixion elements are placed in the distallandmarks to hold the orthopaedic implant, the probe is removed, andthen the proximal landmarks are targeted.

Now referring to FIG. 51, a system 2300 for targeting a blind landmarkof an orthopaedic implant is illustrated. The system 2300 includes theadjustable stop 1801, the probe 2171, and the insertion guide 2210assembled and connected to the intramedullary nail 2155, which isimplanted in a bone B that includes a fracture F. The intramedullarynail 2155 includes a distal aperture 2159 that extends through theintramedullary nail 2155 and is configured to receive a locking fastener(not shown). The probe 2171 is received through an aperture or theadjustable stop 1801, through a cannulation 2210 a of the insertionhandle 2210, and within a cannulation 2155 a of the intramedullary nail2155. The probe 2171 is received within the stop 1801 such that thesensor 2175 is positioned at a known distance from the distal aperture2159. The known distance may range from zero to about 102 millimetersfrom the sensor 2175 to the distal aperture 2159 or other landmark. Inother implementations, the known distance may range from about twomillimeters to about twenty-five millimeters or from about threemillimeters to about ten millimeters. In the depicted implementation,the known distance is about five millimeters.

The system 2300 also includes a tool, such as a drill 2310 that includesa drill bit 2311. The landmark identifier 2016 is engageable with thedrill 2310 and/or the drill bit 2311 such that a position andorientation of the landmark identifier 2016 can be used to determine aposition and orientation of the drill 2310 and/or the drill bit 2311.For example, the housing of the landmark identifier 2016 can include afriction fit engagement with the drill 2310, a strap, or other securingmechanism to at least temporarily secure the landmark identifier 2016 tothe drill 2310. In other implementations, the landmark identifier 2016can be integrated with the drill 2310, or other tool. In someimplementations, the drill sleeve (not shown) may telescope to allow theuser to place the tip of the drill sleeve against a patient and alsoallow the user to move the drill bit in a longitudinal direction fordrilling.

A targeting system 2320 is operable to provide an indication to a user,such as a surgeon, of the relative position of a tool, such as a drill2310 that includes a drill bit 2311, relative to the distal aperture2159. The targeting system 2320 includes a housing 2321, a first sensorport 2322, a second sensor port 2323, a field generator port 2324, adisplay device 2325, and a processor 2327. The first sensor port 2322 isconfigured to receive a connector of the cable 2179 of the probe 2171such that the targeting system 2320 receives signals generated by thesensor 2175. The second sensor port 2323 is configured to receive aconnector of a cable 2214 that is connected to the sensor 2213 of theinsertion handle 2210 such that the targeting system 2320 receivessignals generated by the sensor 2213. The field generator port 2324 isconfigured to receive a connector of a cable 2019 of the landmarkidentifier 2016 such that the targeting system 2320 transmits signalsvia the cable 2019 to control the operation of the field generator ofthe landmark identifier 2016. The display device 2325 is operable tooutput a display of a graphical user interface 2326 that includes arepresentation of the position and orientation of the drill 2310relative to a location and orientation of a landmark of theintramedullary nail 2155, such as the distal aperture 2159, the proximalaperture 2157 (FIG. 50), or another landmark.

The processor 2327 is operable to receive signals from the distal sensor2175 and/or the proximal sensor 2213, and to determine, based on thereceived signal(s), a current position and orientation of the landmarkidentifier 2016 relative to a selected landmark of the intramedullarynail 2155. For example, a feature of a signal received from the distalsensor 2175, such as one or more induced electrical currents, can beused by the processor 2327 to determine a distance of the landmarkidentifier 2016 from the sensor 2175, as well as an orientation of amagnetic moment of a field generated by the landmark identifier 2016.For example, the sensor 2175 can transmit a signal indicative of acurrent value and an identifier that indicates which of a plurality ofinduction coils produced the associated current value. The processor2327 can compare the received current values with reference valuesassociated with each of the induction coils to determine differencesbetween the received values and the reference values. The referencevalues can be values of induced current associated with a referencefield generation signal, a reference position, and a referenceorientation of the landmark identifier 2016. The processor 2327 usesthese determined differences between the received and reference valuesto determine a difference in position and orientation of the landmarkidentifier 2016 from the reference position and orientation based on anydetermined difference in the magnetic field generated by the landmarkidentifier 2016 from the reference field. Based on the difference inposition and orientation of the landmark identifier 2016 and thereference position and orientation, a current position and orientationof the landmark identifier 2016 relative to the sensor 2175 can bedetermined by the processor 2327.

The current distance and orientation of the landmark identifier 2016relative to the sensor 2175 are used by the processor 2327 to determinethe current distance of the landmark identifier 2016 from the distalaperture 2159 and the current relative orientation of the magneticmoment of the generated magnetic field relative to a centralthrough-axis of the distal aperture 2159. For example, the processor2327 determines the current distance and relative orientation of thelandmark identifier 2016 relative to the distal aperture 2159 based on aknown position and orientation of the distal aperture 2159 relative tothe distal sensor 2175. The processor 2327 also determines a currentposition of the drill 2310, including the drill bit 2311, from thedistal aperture 2159 as well as a current orientation of the drill 2310and the drill bit 2311 relative to the central through-axis of thedistal aperture 2159 based on a known position and orientation of thedrill 3210 and the drill bit 2311 relative to the location of thelandmark identifier 2016 and the magnetic moment of the field generatedby the landmark identifier 2016. In the case of the landmark identifier2016, a longitudinal axis of the drill bit 2311 is coaxial with themagnetic moment of the magnetic field generated by the landmarkidentifier 2016.

The graphical user interface 2326 is generated by the processor based onthe determined current position and orientation of the drill 2310 andthe drill bit 2311 relative to the distal aperture 2159, or based on acurrent position and orientation of another tool relative to anotherlandmark. The graphical user interface 2326 includes a first portion2326 a that includes an intramedullary nail image 2155 b that representsthe intramedullary nail 2155 and includes a distal aperture image 2159 athat represents the distal aperture 2159. The first portion 2326 a ofthe graphical user interface 2326 also includes an orientation indicator2330 that includes a first circle 2331, a second circle 2333, and a line2335 that intersects the centers of each of the first circle 2331 andthe second circle 2333. The line 2335 provides an illustration to theuser of the current orientation of the drill bit 2311 relative to thecentral through axis of the distal aperture 2159. Particularly, when thefirst circle 2331 and the second circle 2333 are both disposed entirelywithin the distal aperture image 2159 a, then the longitudinal axis ofthe drill bit 2311 is co-axial with the central through axis of thedistal aperture 2159, as shown in FIG. 51. The graphical user interface2326 also includes a second portion 2326 b that includes intramedullarynail image 2155 b and a drill bit image 2331 b. The current position andorientation of the drill bit 2311 relative to the intramedullary nail2155 is illustrated in the second portion 2326 b of the graphical userinterface 2326.

In use, the probe 2155, the insertion handle 2210, the adjustable stop1801, the landmark identifier 2016, the drill 2310, and the drill bit2311 can be sterilized, such as by autoclaving, if one or more of thecomponents is not sterile. When sterile, the probe 2155 is connectedwith the first sensor port 2322 of the targeting system 2320 and theinsertion handle 2210 is connected with the second sensor port 2323 ofthe targeting system 2320. The processor 2327 detects the connection ofthe distal sensor 2175 and the proximal sensor 2213 and can optionallycause a display of an indication of the proper (or improper) connectionof the probe 2155 and the insertion handle 2210 and/or an indication ofthe proper (or improper) operation of the distal sensor 2175 and theproximal sensor 2213. Similarly, the landmark identifier 2016 isconnected with the field generator port 2324, and the processor candetect the connection of the landmark identifier 2016 and cause adisplay of the proper (or improper) connection of the landmarkidentifier 2016 and/or the proper (or improper) operation of the fieldgenerator of the landmark identifier 2016. The sensor 2175 is connectedto a Programmable Read-Only Memory (PROM) microchip that stores thecalibration values and also stores an identifier that identifies thesensor 2175 as a distal targeting sensor. When the sensor is connectedto the processor 2327, the processor 2327 automatically identifies thetype of targeting contemplated and may display an indication ongraphical user interface 2326 that a sensor of the identified type isconnected.

The insertion handle 2210 is engaged with the intramedullary nail 2155and the adjustable stop 1801 is engaged with the insertion handle 2210.The probe 2155 is then inserted in the adjustable stop 1801 andpositioned at a desired location. The button 1802 is manipulated toallow the probe 2155 to be adjusted, and the button 1802 is released toclamp the probe 2155 in a desired position. For example, the probe 2155can be inserted until a reference mark, such as a printed mark or adetent or other structure of the probe 2155 is correctly positionedrelative to a reference portion of the adjustable stop 1801. Thepositioning of the probe 2155 locates the distal sensor 2175 in thecorrect position relative to the distal aperture 2159.

A drill sleeve 2022 is selected and engaged with the drill sleeveattachment 2020 of the landmark identifier 2016. For example, one of ashort drill sleeve and a long drill sleeve is selected. An indication ofthe selection is input to the targeting system 2320, such as byinteraction with a menu 2326 c of the graphical user interface 2326.Additionally, an indication of the specific intramedullary nail 2155,insertion handle 2210, adjustable stop 1801, and/or probe 2171 is inputto the targeting system 2320, if not automatically recognized by thetargeting system 2320 and/or to confirm the specific intramedullary nail2155, insertion handle 2210, adjustable stop 1801, and/or probe 2171.

The accuracy of the targeting system 2320 is checked before implantationof the intramedullary nail 2155 by placing the landmark identifier 2016directly over the distal aperture 2159 of the intramedullary nail 2155,which can be done by inserting the tip 2024 of the drill sleeve 2022within the distal aperture 2159. If the second circle 2333 is shownwithin the distal aperture image 2159 a, and if the orientation of theline 2335 corresponds to the orientation of the drill sleeve 2022, thenthe targeting system 2320 is accurate. If the targeting system is notaccurate, the input indications of selected components, and/or theposition of the probe 2171 are checked. If no errors are found, then thetargeting system 2320 is recalibrated, as described below with referenceto FIG. 52.

When the components are assembled and checked as described above, theintramedullary nail 2155 is implanted in the bone B. When theintramedullary nail 2155 is located in the desired position, the tip2024 of the drill sleeve 2022 is placed over the distal aperture 2159.When the landmark identifier 2016 is brought near the sensor 2175, asignal generated by the sensor 2175 is received by the processor 2327,and one or more signal feature, such as a current value, and anidentifier are used by the processor to determine that distal targetingis being attempted, and the targeting system 2320 enters a distaltargeting mode. Locating the tip 2024 relative to the distal aperture2159, which is hidden within the bone B, is performed by a user bymaking reference to the graphical user interface 2326 in the distaltargeting mode, and is confirmed when the first circle 2331 and thesecond circle 2333 are located within the distal aperture image 2159 a.

An incision is made in the skin at the location of the distal aperture2159. The drill sleeve 2022 is then inserted into the incision down tothe bone B. The landmark identifier 2016 is then manipulated by a userto arrange both the first circle 2331 and the second circle 2333completely within the distal aperture image 2159 a and, whilemaintaining the position and orientation of the landmark identifier2016, the drill bit 2311 is inserted through the drill sleeve 2022 and auser drills through the bone B, through the distal aperture 2159, to thecortex on the far side of the bone B. A desired drill depth can beachieved by the user by referring to the second portion 2326 b, or bycomparing one or more reference marks included on the drill bit 2311 toa reference portion of the landmark identifier 2016.

The drill bit 2311 is then removed and a locking fastener (not shown) isengaged with the bone B and the distal aperture 2159 through the drillsleeve 2022, again maintaining the first circle 2331 and the secondcircle 2333 within the distal aperture image 2159 a. A desired depth ofinsertion of the locking fastener can be achieved by a user by referringto the second portion 2326 b of the graphical user interface 2326, or bycomparing a reference marking on a fastener driving tool (not shown) toa reference portion of the landmark identifier 2016, as described above.

In addition to engaging the locking fastener with the distal aperture2159, the targeting system 2320 can be used to target a proximallandmark of the intramedullary nail 2155. For example, before or afterengaging the locking fastener with the distal aperture 2159 and the boneB, a user can select the sensor 2213 from the menu 2326 c or move thelandmark identifier 2016 within a predetermined distance of the sensor2213, which causes the targeting system 2320 to enter a proximaltargeting mode and output a display of the relative position andorientation of the drill 2300 and/or the drill bit 2016 relative to aproximal landmark of the intramedullary nail 2155, such as the proximalaperture 2157 (FIG. 50). A user can then engage a fastener or other toolor implant with the proximal landmark in a manner similar to thatdescribed above with respect to drilling through the distal aperture2159 and/or engaging the locking fastener with the distal aperture 2159.

As mentioned above, a proximal landmark can be targeted using thetargeting system 2320 and the sensor 2213 before or after targeting adistal landmark, such as the distal aperture 2159. Particularly, aproximal landmark can be targeted before insertion of the probe 2171within the adjustable stop 1801, the insertion handle 2210, and/or theintramedullary nail 2155. The proximal landmark can also be targetedafter removal of the probe 2171, or while the probe 2171 is insertedwithin the adjustable stop 1801, the insertion handle 2210, and/or theintramedullary nail 2155. For example, as discussed above, the probe2171 can be inserted through a portion of the intramedullary nail 2155that does not interfere with engagement of the drill bit 2311 or thefastener with a proximal aperture or other proximal landmark.Additionally, if the probe 2171 is inserted into the cannulation 2155 aand the proximal aperture also passes through the cannulation 2155 a,the cannulation 2155 a can be large enough to simultaneously accommodateboth a fastener or the drill bit 2311 and the probe 2171. For example,the probe 2171 can be dimensioned to be disposed in a gap between thedrill bit 2311 and an inner wall of the intramedullary nail 2155 thatdefines the cannulation 2155 a. Similarly, the probe 2181 (FIG. 48),which has both the distal sensor 2185 and the proximal sensor 2186, canbe inserted in the cannulation 2155 a and both distal and proximallandmarks of the intramedullary nail 2155 can be targeted withoutremoval or adjustment of the probe 2181.

Alternatively, a proximal landmark of the intramedullary nail 2155 canbe targeted using the targeting system 2320 and either the sensor 2175of the probe 2171 or the sensor 2165 of the probe 2161 (FIG. 47). Forexample, after engaging the locking faster with the distal aperture2159, the probe 2171 can be adjusted using the adjustable stop 1801 tosecure the sensor 2175 in a predetermined location relative to one ormore proximal landmarks of the intramedullary nail 2155. The menu 2326 ccan then be used to select a proximal targeting mode such that thetargeting system 2320 is operable to display a position and orientationof the drill 2310 and/or the drill bit 2311 (or other tool or implant)relative to the proximal landmark(s). Similarly, and particularly whereit is undesirable to have a portion of the probe 2171 extending adistance from the adjustable stop 1801, the probe 2161 can be connectedto the targeting system 2320 and inserted in the adjustable stop 1801such that the sensor 2165 is located in a know location relative to oneor more proximal landmarks of the intramedullary nail 2155. In eithercase, one or more proximal landmarks of the intramedullary nail can thenbe targeted using the targeting system 2320, as described above. Inother implementations, the proximal landmark(s) can be targeted beforethe distal aperture 2159 using the prone 2171 or the probe 2161.

Now referring to FIG. 52, a calibration member 2340 is attached to thelandmark identifier 2016 and the intramedullary nail 2155 for use incalibrating the targeting system 2320. For example, if the accuracy ofthe targeting system 2320 is checked before inserting the intramedullarynail 2155 and errors are found, the targeting system 2320 can bere-calibrated. In use, the calibration member 2340 is engaged with thelandmark identifier 2016. Then a tip 2341 is inserted into the distalaperture 2159 until a reference portion (not shown) of the calibrationmember 2340 abuts the intramedullary nail 2155. Re-calibration of thetargeting system 2320 can then be achieved by interaction with the menu2326 c of the graphical user interface 2326. For example, a“re-calibrate” option may be selected from the menu 2326 c, which causesthe targeting system 2320 to transmit a driving signal to the fieldgenerator of the landmark identifier 2016 and to store as referencevalues any current values received from the sensor 2175 of the probe2171. The graphical user interface 2326 can display an indication of asuccessful re-calibration of the targeting system 2320.

Now referring to FIGS. 53-57, details of the adjustable stop 1801 areillustrated. The adjustable stop 1801 includes a housing 2401 thatincludes a clamp member slot 2402. A clamp member 2411 is receivedwithin the clamp member slot 2402 and is biased by a spring 2413. Theclamp member 2411 is retained within the housing 2401 by pins 2415. Theclamp member 2411 also includes an actuator slot 2417, a linkageaperture 2418, and a probe aperture 2419.

The button 1802 includes an actuating shaft 2421 and an actuating slot2423. The actuating shaft 2421 is received within an aperture 2405 ofthe housing 2401 and is biased against insertion into the housing by aspring 2425. When assembled, the actuating shaft 2421 is received in theactuator slot 2417 of the clamp member 2411 and is retained in thehousing 2401 by a linkage pin 2427 that is inserted into the actuatingslot 2423 of the actuating shaft 2421 through an opening 2403 of thehousing 2401 and through the linkage aperture 2418 of the clamp member2411. In use, when the button 1802 is depressed against the biasingforce of the spring 2425, the linkage pin 2427 is moved within theactuating slot 2423 which pushes the clamp member 2411 against thespring 2413 to allow a probe to be inserted into the hole 1808 andthrough the probe aperture 2419. When the probe is inserted and thebutton 1802 is released, the springs 2413 and 2425 cause the clampmember 2411 to bear against the probe to maintain the position of theprobe within the hole 1808.

The thumb wheel 1806 is received within a thumb wheel slot 2407 of thehousing 2401 and the bolt 1807 is threaded into a threaded aperture 2431of the thumb wheel 1806 through a bolt aperture 2409 of the housing2401. After the bolt 1807 is threaded into the bolt aperture 2431, a pin2433 is inserted through an aperture 2435 (FIG. 56) of the thumb wheel1806 and into a slot 2437 (FIG. 56) of the bolt 1807 to retain the bolt1807 in engagement with the thumb wheel 1806.

Now referring to FIGS. 58-62, details of the adjustable stop 1803 areillustrated. The adjustable stop 1803 includes a housing 2501 thatincludes a clamp member slot 2502. A clamp member 2511 is receivedwithin the clamp member slot 2502 and is biased by a spring 2513. Theclamp member 2511 is retained within the housing 2501 by pins 2515. Theclamp member 2511 also includes an actuator slot 2517, a linkageaperture 2518, and a probe aperture 2519.

The button 1802 includes an actuating shaft 2421 and an actuating slot2423. The actuating shaft 2421 is received within an aperture 2405 ofthe housing 2401 and is biased against insertion into the housing by aspring 2525. When assembled, the actuating shaft 2421 is received in theactuator slot 2517 of the clamp member 2511 and is retained in thehousing 2501 by a linkage pin 2527 that is inserted into the actuatingslot 2423 of the actuating shaft 2421 through an opening 2503 of thehousing 2401 and through the linkage aperture 2418 of the clamp member2511. In use, when the button 1802 is depressed against the biasingforce of the spring 2525, the linkage pin 2527 is moved within theactuating slot 2423 which pushes the clamp member 2511 against thespring 2513 to allow a probe to be inserted into the hole 1805 andthrough the probe aperture 2519. When the probe is inserted and thebutton 1802 is released, the springs 2513 and 2525 cause the clampmember 2511 to bear against the probe to maintain the position of theprobe within the hole 1805.

A threaded bolt 2531 of the clamp knob 1804 is threaded into a boltaperture 2509 of the housing 2501 to secure the adjustable stop 1803 toan insertion handle.

System calibration may be accomplished during manufacturing, afterdistribution, or immediately preceding implant implantation. Thecalibration step is analogous to registration in computer assistedsurgery. Calibration may be needed for different reasons. For example,sensor calibration may be needed to correct for manufacturingtolerances. The system may be designed based upon acomputer-aided-design model, and calibration is used to accurately placethe sensors relative to one another. The processor or the control unitmay include software to generate X, Y, Z, pitch, yaw, and roll offsetvalues to locate the sensors in a global coordinate system or simplyplacement relative to one another. The system may be manufactured andcalibrated during manufacturing and assigned a unique identifier, suchas a serial number, color code, bar code, or RFID tag. If the systemneeds to be re-calibrated, the unique identifier may be used to retrievethe offset values, either locally or over a network. Further, the uniqueidentifier may be used to retrieve other data, such as the size of theintramedullary nail or the length of the intramedullary nail and/or theprobe.

The systems for identifying a landmark may be used for other purposesbeyond targeting blind screw holes of an implanted intramedullary nail.These include, but are not limited to, targeting blocking screws andaligning guide pins. In one procedure, blocking (poller) screws can beinserted into the bone directly outside and tangent to the nail or rod.Targets are shown as two lines on the screen on opposing sides of thenail, such as anterior-posterior or medial-lateral, and offset from thenail at a distance, for example, 2.5 mm. The surgeon aligns the landmarkidentifier to one of the lines as determined by anatomical side where heor she wishes to place the blocking screw. Other symbols or indicia suchas dots, bull's-eyes or combinations thereof can be used as targetsshown on the screen. For this application, devices that are insertablein the medullary canal and instrumented with a sensor or sensors can beused as a means to target blocking screws, including but not limited to,a probe, a reducer or an awl. The depicted systems for identifying alandmark can also be used to align or center a guide pin in both A-P andM-L planes for placement of a lag screw in the proximal portion of afemoral nail. An exemplary implementation of this system may include asensor placed with known orientation and location relative to and in theinsertion handle and/or drill guide and/or alignment jig which isremovably attached to the proximal portion of the femoral nail.

While FIG. 1 illustrates a pocket for affixing the first sensor to theimplant, other structure and/or methods may be used to affix these itemstogether. For example, probes of varying length may be used to place thefirst sensors in the appropriate position as illustrated in FIG. 42. Theadjustable stops 1801, 1803 of FIGS. 41-42 may be used to preciselyposition the sensor 2126 in the implant 30.

While only certain implementations have been set forth, alternatives andmodifications will be apparent from the above description to thoseskilled in the art. These and other alternatives are consideredequivalents and within the spirit and scope of this disclosure and theappended claims.

The invention claimed is:
 1. A method comprising: sterilizing a landmarkidentifier with autoclave sterilization, the landmark identifiercomprising a plurality of magnetic field generating elements mounted toan internal mounting structure; after sterilizing the landmarkidentifier, using the landmark identifier to identify one or morelandmarks of an orthopaedic implant; and after using the landmarkidentifier to identify the one or more landmarks of the orthopaedicimplant, sterilizing the landmark identifier with autoclavesterilization.
 2. The method of claim 1, wherein sterilizing thelandmark identifier with autoclave sterilization comprises placing thelandmark identifier in an environment having a temperature of at least120 degrees Celsius.
 3. The method of claim 1, wherein sterilizing thelandmark identifier with autoclave sterilization comprises sterilizing alandmark identifier comprising a plurality of receiving elements definedin the internal mounting structure, the magnetic field generatingelements being mounted to the mounting structure at the respectivereceiving elements, the internal mounting structure being configured tomaintain a predetermined position and orientation of the magnetic fieldgenerating elements relative to each other during the autoclavesterilization.
 4. The method of claim 1, wherein using the landmarkidentifier to identify one or more landmarks of an orthopaedic implantcomprises: placing the landmark identifier near a sensor such that thesensor produces sensor data based on a magnetic field produced by thelandmark identifier; and using a display of a targeting system toposition the landmark identifier in a predetermined position relative tothe one or more landmarks, the display indicating a position of aninstrument determined based on the sensor data.
 5. The method of claim1, wherein using the landmark identifier to identify one or morelandmarks of an orthopaedic implant comprises: placing the landmarkidentifier near a sensor coupled to an intramedullary nail, such thatthe sensor produces sensor data in response to a sequence of magneticfield distributions generated by the magnetic field generating elementsof the landmark identifier; and aligning a drill guide with an axis of adistal hole of the intramedullary nail based on a display of a targetingsystem that receives the sensor data and that displays a position of thelandmark identifier relative to the distal hole of the intramedullarynail based on the sensor data.
 6. A method comprising: obtaining alandmark identifier comprising a housing and a plurality of magneticfield generating elements that are mounted to an internal mountingstructure within the housing; sterilizing the landmark identifier withan autoclave sterilization process that provides pressure, humidity, anda temperature of at least 120 degrees Celsius; and after sterilizing thelandmark identifier, providing the sterilized landmark identifier foruse in a surgical procedure.
 7. The method of claim 6, wherein obtainingthe landmark identifier comprises obtaining a landmark identifiercomprising a mounting structure comprising a plurality of receivingelements having the magnetic field generating elements mounted on or inthe receiving elements, the plurality of receiving elements beingdisposed on the mounting structure at particular locations andorientations relative to each other; and wherein providing thesterilized landmark identifier comprises providing the sterilizedlandmark identifier with the receiving elements in the particularlocations and orientations relative to each other after sterilizing thelandmark identifier.
 8. The method of claim 6, wherein obtaining thelandmark identifier comprises obtaining a landmark identifier whereinthe mounting structure that has a flexural strength of at least 10,000psi.
 9. The method of claim 6, wherein obtaining the landmark identifiercomprises obtaining a landmark identifier having the magnetic fieldgenerating components mounted on the mounting structure such that theautoclave sterilization process does not change the orientations of themagnetic field generating components by more than 2 degrees.
 10. Themethod of claim 6, wherein obtaining the landmark identifier comprisesobtaining a landmark identifier having the magnetic field generatingcomponents mounted on the mounting structure such that the autoclavesterilization process does not change the locations of theelectromagnetic field generating components by more than 0.005 inches.11. The method of claim 6, wherein obtaining the landmark identifiercomprises obtaining a landmark identifier having a silicone outercovering.
 12. The method of claim 6, wherein sterilizing the landmarkidentifier with the autoclave sterilization process comprises directlyexposing the landmark identifier to the pressure, humidity, andtemperature of the autoclave process.
 13. The method of claim 6, furthercomprising placing: placing the landmark identifier near a sensor suchthat the sensor produces sensor data based on a magnetic field producedby the landmark identifier; and using a display of a targeting system toposition the landmark identifier in a predetermined position relative tothe one or more landmarks, the display indicating a position of aninstrument determined based on the sensor data.
 14. A field generatorfor use in a surgical targeting system, the field generator comprising:a mounting structure comprising receiving elements disposed on themounting structure at locations and orientations relative to each other;magnetic field generating components received in the receiving elements,the electromagnetic field generating components being configured toproduce a sequence of multiple different magnetic field distributions;and a housing that extends around the mounting structure and themagnetic field generating elements, wherein the mounting structure isconfigured to maintain the positions of the receiving elements within apredetermined tolerance relative to each other after the field generatoris subjected to one or more autoclave sterilization processes.
 15. Thefield generator of claim 14, wherein the mounting structure has one ormore recessed portions.
 16. The field generator of claim 14, wherein themagnetic field generating components are inductive coils.
 17. The fieldgenerator of claim 14, wherein the housing comprises a covering thatincludes a silicone material.
 18. The field generator of claim 14,wherein the mounting structure that has a flexural strength of at least10,000 psi.
 19. The field generator of claim 14, wherein the mountingstructure is configured to maintain positions of the magnetic fieldgenerating elements such that autoclave sterilization does not changethe orientations of the magnetic field generating components by morethan 2 degrees.
 20. The field generator of claim 14, wherein themounting structure is configured to maintain positions of the magneticfield generating elements such that autoclave sterilization does notchange the locations of the electromagnetic field generating componentsby more than 0.005 inches.